The age discrepancy was put down to the twins being immediately placed in stasis by the High Evolutionary after Magda left. They were decanted decades later when Bova gave them to the Maximoffs. It was Avengers Origins: Scarlet Witch and Quicksilver that depicted this. It would explain both why Magneto wouldn’t immediately connect the twins as being his despite their eerie resemblance to himself and Magda, and their relative youth as the children of Holocaust survivors.