My best friend just turned 23 and is dating a 30 year old man. I think this is quite weird and it's freaking me out. This man has his own house and my friend still lives with her parents, who for some reason approve of her dating this guy. Does anyone else think this is weird? Should I say something to my friend or keep my mouth shut? I don't want her getting hurt

Honestly, as they are both adults, it is NONE of your business..
Poking your nose in will most likely result in the lose of a friend.

Why is this weird? Why would she get hurt? Seven years between adults isn't a bad spread. My parents were six years apart and married when my mom was 20. My dad died just short of their 50th anniversary. Apparently, your friend's parents have met the man and are satisfied their daughter is in good hands. Relax!

I would just keep quiet if I were you, and figure out why this situation freaks you out.

She is grown. Why does it bother you?

I see jealousy here, she has an appropriate relationship with someone that actually has two pennies to rub together, and you are upset? Sounds like you are jealous.