In terms of mental age/status as a young teenager, what would be an appropriate chronological age for a high elf?

Question

I'm in a campaign where all the players are supposed to be the human equivalent of young teenagers from their villages.

In terms of mental age/status as a young teenager, what would be an appropriate chronological age for a high elf? Due to a running joke with the DM (when rolling up the character I basically ended up with a sort of Captain America type in terms of stats and proficiencies), I googled Captain America's age at the end of his MCU journey, which Google said to be 183. So, whenever we go anywhere as a group the other players roll out the classic Steve Buscemi joke of "What up fellow kids?" because they've not tried to work out the equivalent age for a teenager of their race. When questioned they just straight up say "my tiefling is 16 years old"; in fact, once whilst trying to sneak in somewhere the group ended up running with the idea that the druid would wild shape in to a dog and we pretend its my "assistance" dog because you know I'm old and stuff.

That, and my family is somehow connected with events that happened 300 years in the past.

Answer 1

Young teens, perhaps into mid-twenties.

The Human age entry lists (emphasis mine):

Humans reach adulthood in their late teens and live less than a century. - PHB page 29

Meanwhile, the High Elf age entry lists (emphasis mine):

Although elves reach physical maturity at about the same age as humans, the elven understanding of adulthood goes beyond physical growth to encompass worldly experience. An elf typically claims adulthood and an adult name around the age of 100 and can live to be 750 years old. - PHB page 23

Since Elves reach physical maturity at about the same age as humans, there is some wiggle room. Because they live vastly longer than humans, perhaps about the same age is relative to that longer life. In which case, twice as long wouldn't be radical, allowing for the mid-twenties.

Given your group's joking, and the age of your Tiefling:

You could easily push the age range further, such as into the mid-thirties, which while it should be physiologically undeniable as adult, the Elf's mannerisms could still be quite juvenile.

Real world note:

While modern societies tend to declare adulthood in the late teens to the early twenties, research seems to show brain development finalizing somewhere in the mid-twenties. Perhaps you could apply something like this for Elven declarations of maturity.

Answer 2

This is covered in PHB, p. 29:

Age. Although elves reach physical maturity at about the same age as humans, the elven understanding of adulthood goes beyond physical growth to encompass worldly experience. An elf typically claims adulthood and an adult name around the age of 100 and can live to be 750 years old.

If they reach adulthood at around 100, a young teenager would be around 60-70 years old in regards to status. They would be about 13-15 years in regards to mental age, like a human, as mental development is part of physical aging.