Oh they can get around the whole “age thing” in much cheaper and easier ways than a CGI Batman, or a CGI Superman upper lip.
Case in point, the painfully obvious stunt double being used to bounce off of a trampoline and save the UFP President’s life in Trek VI.
View attachment 1319524
There is no way that the then 60 something year-old Shatner, with an ever expanding waistline (damn the gravitational pull of KFC), could have pulled off that feat. I remember the audience chuckling during that particular portion of the scene.
View attachment 1319528
For an even more hilarious stretch of reality, and the use of an obvious stunt double, watch the “Shatner climbs El Cap in a heavy velour sweater” scene in Trek V.
It would be even easier to put a stunt double in the cowl and cape and double for Keaton, where needed.