I don't think anyone wants them to age in real time, the problem is that they keep them stuck at an age that's perpetually too young to make any sense within the narrative. For me, the O5 should be stuck in their mid 30s, not late 20s. That way, Kitty and the New Mutants can be late 20s, Jubilee and Gen X mid 20s, X-23 and the Academy X kids early 20s, and the Maxime + Manon era of student characters as teens.