A 15-year-old in those times would know how to build a cabin, farm, fix a wagon, and hunt, A 15-year-old in those times would be getting married and starting families.

They got a lot done and educated themselves really fast back then. Schubert wrote 800 songs before he died in his mid thirties, and much more music, not long after these guys.

The founding children

At 21 I'd have supported a communist revolution. Same now, actually.

Wow, that's fascinating! Because of the nature of society then, they would likely have been more mature than today's youths; but the brain doesn't fully develop its self-control mechanisms in males until 27. In women it's 25.

17th century male life expectations was 35-38 (average) so these ages are not out of line.

We were a young vibrant country then and so we're our leaders. Now we're are just old and tired and have lost our imagination and vision. Sad.

There were young men fighting the war and it's interesting to see, but later: President Monroe age 59 President Madison age 58 Life expectancy was younger, but childhood diseases driving down the average age at death. Once someone makes it to 10 or 20, they tended to live longer

Life expectancy was below 40. So, your point is not fascinating at all.