I know I’ve answered this one before, but according to Joseph Campbell, knights would be apprenticed as a page at 7, they’d be promoted to squire at 14, and finally be knighted at 21. (Michi thinks it’s from The Power of Myth, but she’s not 100% certain.)
From there, the question is just, how hard does he need to work to earn the respect of his peers, or to earn some kind of renown? I’d say something like 5 to 10 years beyond that (from 26 to 31), but that’s a mostly arbitrary guess on my part.
-Starke