Gemma Chan as 90's Psylocke is a type of perfection in casting rare to find. That said, she was in a minor role in CM, and is a hair on the older side to just be starting off in such a role(5 years hence). It's too bad the Fox-Men films were such disasters. Gemma would have been a magnificent Betsy Braddock in lets say Apocalypse*if that movie wasn't crap. It's a little too late now for her.
Overall that cast is intriguing in certain aspects(Tom Hardy as Wolverine would have been great too, but now he's Venom), but as others have pointed out, they are too old overall. Yes, the MCU has had older heroes(54 year old RDJ), but they also have younger heroes(23 year old Tom Holland's Spider-Man). I think for the X-Men to have maximum impact as characters, they should be as close as possible to their initial manifestation as possible(so, I'm aiming for early college age at oldest), so we don't have to explain their absence from all those pivotal MCU moments. If you introduce X-Men who are already in their 30's or older, like, where have they been for the past 20 years? I would cast Magneto/Xavier as the 50 somethings, and do the X-Men as college students attending Xavier's Institute for Higher Learning or whatever.
It makes better sense for them to be living with the Professor if they are college aged, and with that 5 year time skip built into the MCU timeline post-Endgame, you could even make it so that they were like, barely manifesting children(12/13) when the Avengers were loosing to Thanos in Wakanda, but are now 17/18, having been training with Xavier in relative secret for a few years when we pick up on their missions(let's say a Krakoa type event where the young O5ers are captured and Xavier recruits the global team including Logan and Ororo to save them).
It is very interesting to wonder at how exactly Feige will introduce them when it is time. The possibilities are endless.