On one hand, I think I'd say 24-25 or something like that. Young, but still an adult. I feel it's an approriate age to do things like get married or pregnant, I could still seek to learn new things, and I'll be old enough to do things like driving and stuff.
But on the other hand, I kinda wanna say 7 or something like that. Because at that age I didn't worry about any of that other stuff, cuz I'd be a child and just wanna play.
It's hard to say to be honest.