I usually have lots of peasants with no labor skills at all (or very little) but I don't mind. I generally use worlds with a history around 100 years, so I kind of expect them to be mostly unskilled if they are not some of the first dwarves of the world. A longer history will produce more skilled dwarves as the population rises, provided your mountainhome is thriving. A mountainhome with 1-3 spots on the map won't send the same quality dwarves as one with 20+ spots on the map. I tend to use the smallest mountainhome, as it's usually the only one already at war with something.
What I do with unskilled dwarves is set them as drones/haulers, who have around 40 labors enabled. Any workshops that they would otherwise have access to (like mason) will have a minimum skill setting so they can't use it being unskilled. This will let me have a mass army of wall and floor makers without ruining the workflow with crappy goods. They also get any and everything else done that the skilled workers won't have time to do. Works nicely. It's also extremely easy to manage everyone.
These haulers are also my expendable military. I don't rely on any of them for quality jobs, so it's no loss if they die defending the fort from early invaders. Later on they will train off and on if they are intended to be melee. Crossbows train by massing invaders with bolts. In a longer battle, they will take shifts once some of them get hungry. That way there's always dwarves firing bolts into enemies. Even as unskilled masses they can stop early sieges in it's tracks just by the sheer number of bolts they put out. If they don't get a lucky strike they'll injure enemies so bad that they can't do anything and bleed to death. The only real threat to them is goblin archers, who usually end up killing some of them before fleeing.