I dunno, I prefer a mostly younger group.
I like the reasoning that mutants have always been around in the MCU but in incredibly small numbers. So you’d have a few adults like Professor X, Magneto, Wolverine, and Sinister who have been operating in the shadows for awhile. But then the events in IW and Endgame triggered an uptick in mutant gene expressions that’s most prevalent in young adults.
So I’d prefer a Professor in his 40s who’s only been running his school for a few years. On the older end you could maybe have Scott, Jean, Ororo, Hank, and Warren as the first graduating class on the older. On the younger side is Kitty and Jubilee. Bobby and Rogue somewhere in the middle. Pepper in other mutants throughout.
I see X-Men feeling like a combination of Stranger Things and Dune in terms of the young adult approach.