If you go by "on screen only" as canon, then certain other things are (or were) canon only by convention.
-- Kirk being from Iowa was held as convention, but not canon until Kirk said so in TVH.
-- The Enterprise being built in 2245 (in TOS) is convention, but it's actually never appeared on screen to become "official" canon. (Indeed the only reference to its age is in TSFS, where it's said to be a 20 year old ship, which raised cries because that's too young to make sense.)
-- The character in question here is conventionally canon, but he could still be tweaked to be whatever anyone wanted him to be if he is finally granted that precious screen time. Including his age and being the captain of a previous Enterprise. So, I'd just go with it.
Or most likely, it's not him at all. Or, it's Weller's character, and he's a hero in the movie, not the villain. Every time we think we know more, we really have only more to speculate on.