Then I was thinking (mostly of the weirdness factor), if I was a father and had a younger friend, would I want them dating my daughter?

About the only way I can relate is I hire undergraduates to work in the lab. And about a year ago, I had a single female student (tall, like 5'11") working in the lab. And I set her up with one of my younger bagpiping students, mainly because he is 6'4".
He would see my party side, she saw my work side, I was privy to both their lives. I would get TMI about their love life. ACK! It just sort of kooked me out.