So we have toddlers, children, Teens, young adults, Adults and Elders but I think we are missing a stage from 16/17 to about 20 you are at an odd stage you are not a kid anymore and not a teen but you...
That's what a young adult is. >18. Realize any addition of more ages takes away from the current ages and teens, toddlers, elders, and even kids are already lacking. So, no. No additional ages are needed.