Hi my sister turned 17 in December, and she is currently seeing a guy who turned 21 a few weeks ago. I have no problems with it at all, neither does anyone else I talk to, but his mum is really upset about the age gap and my sister gets very upset about this. It's only 4 years after all, and of course they are both consenting. She is very mature for her age too.
Any advice I can give to my sister? I really don't want her to be upset but I'm not sure how to make her feel better.