18 yr old with 34 yr old?

My daughter turned 18 in March. She had my granddaughter at 15, since then she's had endless motivation. Graduated early, started college, working. She moved out at 17 and since then has been thriving. She's very mature, and I understand that. But I'm not sure how to feel. We had a family bbq and she asked if she could bring a few guests. I said yes. She shows up with a man, his 2 children, and my granddaughter. She introduces him, his kids, and tells me they've been seeing eachother for awhile and thought it was time to tell me. He was very polite and respectful and they seemed happy together. I figured he was older, but at the end of the get-together my husband asked how old he was. When he said 34, my husband flipped out. We've been arguing like crazy since. I think it's absolutelty fine. She's an adult, she can make her own decisions. This man is a doctor, it's not like he's a bum! I understand the age difference.. I'm just at a loss. I can't find it anywhere in me to agree with hubby. What do you guys think??