Claremont's X-Men for the MCU
Actors are picked for how I would cast each character at the time of their introduction, and assuming that they are the age they are as of 2025. Some are playing younger, others fit the range already.
But this is for my own screenplay I'm writing for fun, and it's due to plans I have for it that Beast is the only character to have different actors playing younger and older versions. Well aside from Destiny, but that is biblically accurate anyway.