I’m surprised he’s 78 but not too worried that that’ll weaken his performance. According to IMDB, Stewart lost 21 pounds for the movie “Logan” [0] in order to portray a sickly Prof. Xavier. Dropping weight as a wrestler was incredibly painful even as a HS wrestler, so I think he must be very healthy for a man in his late seventies to even consider such a regimen.

If anything, Stewart’s old age will be an asset. The final TNG movies had him acting as an action hero; now the new show will be inclined to have more cerebral conflicts.

[0] https://m.imdb.com/title/tt3315342/trivia?ref_=m_tt_trv_trv