Well it depends I guess, on the individual and what role playing experience you want.
I'm 20 right now, I've been studying martial arts since I was a kid, been in a few scraps, I work out, stay in shape, and I'm pretty worldly. My anologous Tamriel self would probably be able to fend for himself. Could I take on the Oblivion horde? Well maybe not now. After a game full of adventuring? Most likely. So do you want to start the game out relatively experienced, or do you want to start with a character who can more or less fend for themselves, and then grow into a more heroic role?
There's the subject of physical health, as well. There's a window of physical prime- you have to be old enough that your body can still heal and take a beating over and over again and still get up the next day without soreness, but old enough that your body has spent time developing muscle- but then there's that day when you wake up and can't move, when the day before you were fine, and that's when you know you gotta take it easy.
An older character, though still strong, but might not be able to fight all day, well, he doesn't have to. He's experienced enough to know when he's got to fight and when he doesn't have to. Younger guys can fight harder, but older guys can fight smarter (think of your old kung fu master, he beats up the young guys because he's experienced enough to know what their attacks are going to look like and where to hit for the most pain).
So really you have a wide range of capabilities depending on the person and who you want to play.
Young, physically fit guy who can take care of himself, but who will grow into the role of hero who can take care of others? (or villain who can "take care" of others...)
Slightly older guy in his prime who's seen some action and is on the top of his game every day?
Old dog who conserves his energy waiting for the young guy to stop showing off so he can shove a sword into his gut?