If nothing else, it'd probably be possible to develop some kind of raw-generating program using templates without as much effort as it'd be to have the game recognize the same templates.
OP: General criticism that comes to mind is that cultures appropriate each other's inventions really readily (you can count the number of times writing has been developed independently without taking off both shoes IIRC). So technology doesn't stratify a great deal - just like present Earth, every culture sharing a continent with an ironmongering culture will use iron whether or not they've developed agricultural expertise. Dwarf Fortress actually makes this distinction really easy to describe: you can buy or steal the same goods no matter what, but you have to have a local/transplanted tradition to use specific skills. I'm going to try and translate that into each of the periods you've laid out.
Other general criticism, although unfortunately pretty much forced due to how weak group diversity is versus race diversity ingame, is the general scifi/fantasy trend to assume a species-culture equivalent. It should be possible for one group of kobolds to live and die by the atl-atl and another to sling nuclear weapons at each other.
Hunter/Gatherer: As primitive as can be, this Civ only has the ability to construct basic implements from wood and stone, hunt, gather herbs, wear clothes (from fur/skins), and bury their dead. They have a language, but no alphabet, and a basic tribal society that can work together for mutual defense/profit. They're lead by the strongest warrior in the tribe.
Examples include: giants, cyclopes, sasquatch, various beastmen, etc.
In addition to the skills provided, hunter-gatherers should also have all the non-glass craft skills - they should have a limited range of items producable, but they can still form various necessities out of all kinds of materials, including soft metals (either in the form of nuggets or melted by fire). This mainly means lead and precious metals. If there were any possible way to introduce artificial skill-level caps, this would be where you'd want to - the single most interesting thing about hunter/gatherer societies is the poor division of labor, and the population wouldn't ever really exist to support someone who just carved bones instead of sticking things between the ribs for them.
They should also all have a couple of domesticated animals - mainly dogs and birds, but possibly other small ones or even horses. Animal care and training should be available.
Stone Age: Slightly more sophisticated than Hunter/Gatherers, this type of Civ can make pottery, weave, construct sophisticated stone implements, and add on to existing structures (including caves), but not build freestanding structures from scratch. They can also farm (poorly), brew alchohol, and may have a sophisticated religion/beliefs. They may have a primitive written language, but literacy will be rare. Basically, this is a "hunter/gatherer" society that has settled down. They may be led by a "council of elders"/republic, a theocracy, or a dictator/monarch.
Examples: Antmen? Trolls? Ogres?
I'm not sure I'd support the 'no free-standing structures' thing - even primarily cave-dwelling groups with advanced stone tools (which is where this cutoff is, BTW - hunter-gatherers typically had a wide range of stone tools, but were mainly limited to certain types of manufacture). I think this would be the best point to introduce carpentry and masonry, and also furnace operation. (Mainly because of magma - they couldn't build or operate coke forges.) Wood burning and potash making are both practiced to some degree for fertilizing purposes, broker skills and nobles have developed (as you rightly point out), and general skill caps should be around Great. Everyone outside of the nobility has farming or threshing as part of their lives, and specialization is rare but certainly possible. Architecture not available, or limited to migrants. Animals transitional between later and earlier phases.
Copper Age: This is a stone age civilization that has learned the techniques for cold-forging (mainly copper, silver, and gold), sophisticated trade (coins, as well as extensive barter), and empire-building. Scribes are employed, and widespread slavery may be an institution. Freestanding structures can be built. Cities can potentially exist, but they will be primitive. Swords cannot be made at this point, only long knives. Traps are limited to stonefall traps, and plate armour is not possible.
Example: Kobolds.
All about right here, although again I'd advance metalworking a tad, and cities as DF players are familiar with started existing long ago - the copper age is the beginning of the polis as
we're familiar with, and they were fairly sophisticated. This would also be where bows worth using would start originating, along with crude crossbows. Expertise (up to grand mastery) would be common.
If we accept that metalcrafting existed before to some extent, this is the point at which it would allow for weapons and armor, exclusively of copper, and charcoal would be a major industry. Crude glass is remotely feasible, and architects should now exist. This is also the beginning of the era of the professional warrior - in the prior ages they'd be largely nobles and their servants. By now, every animal and plant that dwarves currently have domesticated should be tamed and/or domesticated if available.
Bronze Age: A Civ that has learned to forge bronze, and hotforge copper, silver, gold. They can also coldforge iron, if it's available, but cannot make steel, or high quality iron. Long swords cannot be made. They know how to mine, although this will remain a crude, slow process, and can Strike the Earth (make Fortresses), although this also will be labor-intensive. Cities are now complex affairs, and armies/militaries are starting to appear. Religion is at it's height. Medicine has achieved some complexity and sophistication, but is still not fully realized, or separated from mysticism/superstition. Large-scale building projects may be undertaken.
Crossbows, catapults, and ballistae are now possible. Alchemist shops may be built. While it's possible to make green glass, gems/glass cannot be cut.
Example: Titans? Elves (a special case, since Elves would have sophisticated "technology" in separate areas).
You've pretty much got this one down, so here's the big omission instead: pastoral civilizations, which take a trajectory generally parallel to the Civilization-style progression of metals and technology. Nomads' level of technology (especially with respect to metals) is directly related to their neighbors', with the big exception of riding and hunting tools. Starting with the bronze era, pastoral societies begin developing complex, rigorous structures beyond the tribal level; develop composite, laminate, recurve, and other sophisticated bows, and will from thence forth remain a serious threat to sedentary civilizations until the Industrial Revolution turns their slight population disadvantage into complete ruin. The cities will be bribing or running in fear from the nomads from here on out - in part because they develop skills concurrently. In effect, as they train in riding, animal hunting, animal care, and social skills, they're developing military skills. In short, every member works basically the way ambushers or woodchoppers do, and the competitive advantage is incredible. The most dangerous (and thus relevant) nomadic societies were basically semi-barracks-societies, and for dwarves as we know them would pose a HUGE problem -- for any cavalry combat skill, nomadic fighters have basically been in training their entire lives. Elite bowmen, throwers, spearmen, and wrestlers would be the equivalent of Legendary-10+ or better.
Long story short, unless some way to bribe them is in there or you just happen to have a LOT of magma, they're best left well alone.
Iron Age:
The highest level of sophistication. This Civ can hotforge iron, and *might* be able to forge Steel/HFS, if they have the species trait for this. Weapon traps are fully realized, magma forges may be built, and tunnelling may be used during seiges. Barter is being replaced with currency, and government is becoming more and more beurocratic.
Example: Dwarfs, Humans, Goblins
Worthy of note that Iron Age civilizations' forging steel was dependent on the availability of vanadium-rich ore present in Damascus and Wootz steel, and HFS would be preposterous with any temperature reachable outside of magma.
Especially for dwarves, I'd bump back incidental or low-intensity metalwork by an age or more each (remember, neither iron nor steel was 'invented' the way the telephone was; they were discovered independently various times, first hewed from meteors or obtained as native or decent ores and basically worked as hard, useful stone, and by the time people were able to set up forges to build weapons out of it from scratch the same was being done (more or less) with steel. I think the only good way to explain dwarves' fairly extreme period-relative stone- and metal-working prowess is a very different cultural evolution. They'd be playing around with carbon allotropes as soon as they discovered the microscope, and would probably have working superconductors well before they invented the internal combustion engine. Dwarven evolution would rhyme with human, but they're not the same thing.
And again, THE big deal is what skills are available, how freely they can be trained, and how skilled someone could hypothetically get (without divine inspiration, that is). It's all basically the development of society's ability to form bureaucracies and castes and divide labor. Technology and goods are mainly incidental. Pretty much every society crosses those phase transitions somehow; some of them did it when humanity was first toying with bronze and some of them did it after man had set foot on the moon.