Except nothing was really retconned. It's long since been established that there is a sliding time scale, and the original X-Men were, what, 16 when the team formed? 13 years on would be about right. Paide was about 15 or 16 at the start of Gen X, as far as I remember.
If she was twenty five and he was thirty five there would be less of an outrage, as it was there was nothing illegal or really wrong with the situation. The ages shouldn't be the issue, the bad writing and air sex in front of her mother are the real problems.