Considering Kuno being 17 would graduate Furinken in a year I would tell you that they stay the same and don't age. I can't deny that Takahashi changed the way she drew them over time and they did start to look older. Anyway, it was just convenient story telling like in The Simpsons. Ranma turned into filler shit in the last few seasons, You would be better off reading the comic.
Knights
It's like Dave's RAB, he's stated that they're in a continuous loop and no matter what they do, they'll be the as ever at the beginning of each episode.
Gendo
Damn you, time-hating fictional universes.