Xavier wasn't originally meant to be much older than the Original 5. That changed later when they filled in his backstory more. Plus if Jean was 17 she wouldn't be underage regardless. Yeah it's still a bit creepy on some level but the only one who was really underage by a large margain was Iceman. And yeah, I prefer furry Beast by a longshot. That's why when I have him get deaged even in RP I don't have him lose that aspect.