For me:
Babies: around 9-12 months
Todds: 1 to around 4-5 years
Children: 5 to 12-13-14
Teens: 13-14 the youngest to 18
YAs: 18 to 30-33 (sorry, anything older is adult)
Adults: 30-33 to 60-65-70
Elders: from around 60-70 to death.
For me the gap between the child and teen stage is a bit too much. Here I would like to see an extra age category like a pre-teen stage. For me the children are only to like 11-12 years old and the teen stage is 15-16 to 18. I play on the longest lifespan so I solve it by dressing the newly transitioned teens into outfits best suited to 13-15 year olds then around the middle of their age span their outfits will resemble more towards what teens and adults wear.