Relationships

So ladies I need yalls opinion. I have been talking to this guy I've known for four years now. He's 30 and I'm 17. He recently asked me to be his girl. I said yes but I haven't told my mom or any of my family because I know they wouldn't agree with that. I have a friend who is 18 and she dating a 35 year old and my family shames her for it. What should I do? Should I tell my family? Also am I doing right by being with him?