Seeing as DF has a tech cap of 1400, we can posit that humans would be of similar height to what they were pre-renaissance. Due to poor nutrition and other factors most humans were only slightly above five feet tall. In the Bronze Age 5 foot 4 was considered large. Take from my random knowledge what you will.
I'm pretty sure they also weighed less than 70kg during that time. When humans switched from hunter/gatherer to primarily subsistance farming, lack of dietary balance made them smaller and less healthy overall, and it has only climbed back up to the larger prehistoric heights human reached gradually as nutrition and food supply have improved in the past two centuries. 70 kg as an average mass is pretty recent.
Some nations, especially Scandinavian nations, tend to have the tallest/most massive/healthiest people thanks in large part to diet, and are larger than that average, while less developed nations with limited diets tend to have shorter people, and peoples who have been locked in islands for many generations tend to be smaller and shorter, thanks to "Islandification". Men also typically outmass women by about 5 to 10 kg, although this isn't related to health.
Basically, if we were being really accurate, the humans in this game, who are now mainly subsistance farmers, should be less massive and shorter with the possible exceptions of the better-fed noble classes. Humans who live on more balanced diets of whatever plants they scavenge from the wilds and plenty of fish would be more massive, as well, which would basically be people who lived as bandits or hermits from birth.
Not that I havent' done WAY too much research on all this crap, though...
Elves can probably be thought of as similar to something like the islandified people - they live more by foraging, and while they don't have limited landmass, their limited food gathering methods for the abnormally high density of population they let live there means that they might have a slower or more adjustable metabolism (basically, they could develop some means of hibernating or entering a more languid state to conserve energy) since they tend to be fairly nimble while in danger, and they would simply be smaller to conserve the amount of body mass their food needs to support. Being smaller is problematic for warm-blooded creatures like mammals, however, because it means you have a lower mass to surface area ratio to preserve body heat, and hence, more energy is spent keeping yourself warm. They would need to either stick to warmer climates, or have some method of languid or hibernative state where they could surive conserving energy.
Dwarves, meanwhile, I've always thought of more along the lines of the Neanderthals. They're shorter, stockier, better suited for slightly colder climates because their bodies are more compact. They have short legs that make them poor long-distance runners, and poorly adapted for open plains, but they also have powerful upper body strength, and can make great ambush hunters where their slow speed and poor running stamina isn't as much a problem.
History Channel had a special on it, speculating that early humans would have competed with neanderthals over food resources, but while humans hunted with bows, neanderthals hunted like true dwarves would - they attacked the biggest, most dangerous game they could find (wooly mammoths, basically, elephants) by jumping on its back from ambush and trying to hack its throat out with a sharpened stone spear before the mammoth could toss the neanderthal off, and gore him/her horrifically. Remains of neanderthals were examined to reveal hunters often broke multiple limbs on multiple occasions and had several wounds that implied they had been impaled in major organs in their short, violent lives.
Long story short, neanderthals were the real-life dwarves.