Friendly reminder that although you can homebrew it to be like this if you want, in the official D&D 5e lore, Elves and Dwarves mature at the same rate as humans, so they’re all adults at 21.
Culturally is a little different, much like some older humans still view people in their 20s as “kids”, elves and dwarves will only consider themselves to be truly adults after at least 100 years or so, but that’s just a social stigma, not how they are biologically.
They grow into adulthood at the same rate as humans, but after that point they age at a slower rate.
As per the PHB, page 23:
And page 20:
So i did get some things mixed up, for Dwarves it’s 50, not 100. Same idea though.
I know it sounds weird at first, but It actually makes a ton of sense. I mean, even outside of fantasy, the amount of time an animal takes to reach maturity isn’t really proportional to how long it lives, it has more to do with its intelligence, which is about the same for all D&D races. For a lot of animals, reaching full maturity only takes a couple of months tops. Turtles can live way longer than humans yet they mature in about 5 to 8 years depending on the species.
Humans are already pushing it with about 2 decades worth of growing, having to spend a literal century as a kid, especially in a world as dangerous as the forgotten realms would be insane.