A lot of people have made some version of this same point. But you’re not thinking it through–this doesn’t solve anything.

The way Marvel Time works, it’s only been around 13-15 years since the Fantastic Four got their powers and the Marvel Universe was born. This is why Cyclops and Beast and Iceman aren’t 70 years old. And it’s a sliding situation–next year, it will still have been 13-15 years, and more and more accumulated history is crammed into that container that only grows very slightly over a long period of time.

So this means that X-MEN #1 happened, give-or-take, around 2001. And that means that, if Magneto was a child of let’s say 12 when he was in the Camps in WWI, then he was 67 years old when he first fought the X-Men and founded the brotherhood of Evil Mutants. And next year, he’ll have been 68. And the year after that, he’ll have been 69.

The problem is that his Auschwitz experiences are a fixed point in time, but his super villain career is a floating point in time that always moves forward along with the rest of Marvel history. So yeah, Magneto was reduced to infancy and then restored–but that happened well into his career as a villain. Very soon, he’ll have been a 90 year old man taking on those punk teenaged X-Men for the first time. And Professor X is already close to half Magneto’s age.