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[Marvel Universe] Based on his major character origin, how the hell is Magneto still alive and present if the Marvel universe supposedly takes place in modern year?

So I was wondering the other day about how while DC tends to reboot their characters in order to keep them up to date, Marvel’s characters seem to be more flexible in updating, such as having Tony Stark become iron man during the Gulf War or saying Peter Parker went to high school in the 2000s rather than the 1960s. Then you have characters like Captain America, who’s history in the golden age stays the way and only updates when he unfrozen onward.

Then, I got to thinking about Magneto... I know he’s been retconned in the past before, especially with his relationship to Quicksilver and Scarlet Witch, but a major character point for him is that he was a holocaust survivor and witnessed the horrors of humans, which built into his belief that mutants are the next step. Unlike most marvel characters, I feel that’s something you can’t change about him, which becomes a problem when Marvel acts as their stories always take place in modern year... so Magneto would have to at least be in his 80s by now. I get that it’s comics and he could still be pushing it at 80, but there’s gonna come a time when he’s pushing 90+, 100+, etc. Then you have the fact he and Xavier are still peers, so then Xavier will have to age as well. I’m curious as to what Marvel would do come the time they’re both ridiculously old, even by comic book standards.
gpt
In Defenders #16 Magneto created a being called Alpha the Ultimate Mutant.  Alpha de-aged Magneto to infancy.  He was restored to adulthood later, but restored to basically have the body of someone in their 20s while keeping his mind.  He's aged normally (-ish, Magneto is inhumanly fit) since and is now ~50-60 physically. 

So he is very old, but through these types of super-powered shenanigans his body doesn't necessarily reflect that.