Something which occurred to me after reading X Lives/Deaths of Wolverine.
Now Ben Percy cleverly avoids using any exact dates for events like Xavier's birth which would logically fall under the ambit of the floating timeline. But we do get precise dates for some events naturally.
The one thing which is crystal clear is that, going by the timeline of Wolverine's life established by this story, Charles Xavier was born after the end of WW2.
Logan saves the life of Brian Xavier (Charles' father) as a young lieutenant during WW2. Logan's life with Itsu in Japan (which led to Daken's birth) is said to occur 'post-war'. And Charles Xavier's birth is very clearly placed after that in the timeline.
Now, let's assume that not a lot of time passed between Logan saving Brian Xavier during WW2 and the birth of Charles. Let's say it was just around 5 years or so. Even so, the earlier birth year Charles could logically have is sometime in the late 1940's/early 1950's. Which would still make him a good 20 years younger than Magneto, who's established as being born in 1928 (as per the Magneto Testament series). Even if we don't take that particular date as sacrosanct, he can't be a lot younger than that...we know he was at least a pre-teen while in the camps.
Xavier and Magneto's ages relative to each other is one of those problems with the sliding timeline that is only going to get worse as, ahem, time passes. If we go by what I've explained above, the earliest Xavier could have traveled to Israel as a volunteer helping Holocaust survivors would have likely been in the early-to-mid 1970's, when he'd be a young man in his twenties. And Magnus, whom he would have met there, would already be well into his forties and virtually old enough to be Charles' father!
It does change the complexion of their relationship somewhat - them not being contemporaries or having the same or similar amount of life experience when they first meet. Though I suppose it makes it easier for Magnus to dismiss Xavier's dream as 'youthful idealism'. But then that's not why he originally dismissed Xavier's dream, so it also changes things.
I dunno...what are your thoughts on this?