Warren Ellis has gone on record as stating that as far as he was concerned Kitty was older than 16 when she and Pete had sex (I can't recall if he said he thought she was 18, but may well have done) so she was never under legal age. As I recall, it was Claremont who later de-aged her when he came back to the X-titles.

As someone whose favourite character was Dick Grayson, I was VERY used to the concept of telescoping time.