When I was 28, I dated a 19 year old. In retrospect, it was kind of cheesy (especially her telling her parents I was 24, and me going along with it). But at 28, I was pretty immature and not really ready to settle down and be in a serious relationship, so a typical 19 year old girl was probably a better match for me than a typical 28 year old woman.
My mom and mother in law both married at 20 or so and their marriages both lasted, but that was a different time. My wife married at 18 and was divorced by 20.