My d&d character Kairon is 38. Tieflings have a lifespan just a little over that of humans so he's not particularly young in the scheme of things. I've drawn him a bit young-looking for his age unfortunately, whoops.
I haven't fleshed out his emotional development that much yet, but he's happily adventuring on the search for more books to add to his library. He wants to settle down once he's in his 50s or so, but for now he's having fun.