Alright so messing around in the raws
I've found this [BODY_SIZE:0:0:3000]
[BODY_SIZE:1:168:15000]
[BODY_SIZE:12:0:60000]
I was wondering if it's possible to have your dwarfs be children or start having them work in the fort faster? (I like to think it'd be kinda cool having a group of children running off into the wilderness to start their own fortress)
Would [MAXAGE:150:170] help?
Neither of these affect whether a child can work or not. I don't believe that you can make children work by changing the raws, though Dwarf Therapist can allow you to make children and babies work, IIRC. I haven't used it in a long time, so I'm unsure if it still does that.
BODY_SIZE is how large they will be at specific ages. The first argument is their age in years, the second is days, and the third is size. So [BODY_SIZE:0:0:3000] means that they will be size 3000 when they are born, [BODY_SIZE:1:168:15000] means they will be size 15000 at one year and 168 days, and [BODY_SIZE:12:0:60000] means that at age twelve they will be fully grown.
MAXAGE is the youngest and oldest possible ages a dwarf can die of old age at. No dwarf will die of old age before they are 150 and no dwarf will live longer than 170 years old unless affected by something such as vampirism or other syndromes or interactions.
The only other tags that affect children or babies are ones that change their name and ones that set how long they will be an infant/child for. BABY:1 means they are no longer a baby once they are one, and CHILD:12 means that they reach adulthood once they are twelve. By lowering these you can make them mature and work sooner. You can remove the baby token to have them be born as children, just don't remove both tokens, as otherwise children cannot be born.