ofc his mother is a demon or something

Considering it's something that has been w the family for generations, I'd guess the Demon would always switch hosts when it came the time for it. Or I'd hope, I think that would be cool, i feel it's been a while since we've seen talks of demon possession and have gotten demons in disguise instead ╮(￣▽￣)╭

Omg I thought the same thing. Or there a servant of the family that the demon and either use magic to make other not notice they did age or change host