Age Gap

So i’m 15 and my bestfriend is 14 (we practically grew up together) and she’s dating a 17 year old, she is honestly really mature for her age because she has older siblings and her boyfriend is a little childish and looks younger than he is i know my generation normally dates guys that are a little older but i just feel like it’s kinda wrong, her siblings are all really mature and her sisters are big feminists i think and they think it’s fine because of her maturity and she doesn’t look her age and no one can picture her dating someone her age because they aren’t going to be mature enough for her, her sisters are older then 21 and one of them was even 16 when she dated a 22 year old except she’s the one that tried to get with him, so do you guys think i need to have a talk with my friend? i know they love each other but i don’t know if it’s right they’ve been together like 5 months now and he’s met the whole family i want to be happy for her but idk.