Well... Here is what I have to go by: DP and I met when I was 17, we have 11 years difference. Couldn't have been happier for the past 10 years.
* he is, handsome, supportive, funny, patient, doesn't mind cooking dinners, is romantic, I would consider that a catch
* he never pressured me sexually, if it wasn't for his standards, I wouldn't have waited until I was 18.
* he did drink socially, but I never did outside my family (we both have European roots, and neither family would frown upon a teenager having a glass of wine or beer); neither one of us ever been drunk, or driven a car after drinking. He never bought me a drink until I was 21.
He is the most wonderful dad to his now 15 y.o. daughter who lives with us. And yes, my parents were very cautious about him in the beginning, but they love him now. In fact, my mom calls him "her favorite son in law", and we are not even married (yet)
It's very much a US thing to judge a couple by the age (I think). One of my sisters is happily married to someone 9 years older than she is. They have three kids, and as far as I can see, her and her husband fit each other to a T (and not the "trouble" kind).
So... I can't say I wouldn't be worried, but to tell you the truth, I think I'd be worried no matte who dsd chose to date.