This suggestion is to add a new sprite for villagers when they reach "teen" status. For me personally, I like to save before they reach adulthood so that if I dont get a good trade, I exit and reload until I get something that suits me (much like I do when trading, their next tier should be something useful to me)
Having teen status would help those like me, since they would have a better idea on how long it will be until they reach adulthood, not to mention would block them from finding ways to go into 1 block areas (and subsequently suffocating themselves with age boost). Teen status boost would shove them from such spaces
Also would give a nice feel to the game, having little adults roam around.
Alternately, they could trade some lesser useful trades as "training traders"