In my opinion, age doesn't matter. Like someone else said in this topic, it doesn't matter if it's love.
I'm 20 and dating a 27, going on 28 very soon, guy. It's not much of a difference, but if you think about it, we're at different stages in our lives. Although, I think our relationship is different than others only because we see eye to eye on almost everything. Almost. (; And many other things that I cannot explain. I can also see age related issues at times. They are not HUGE problems, if they were then we wouldn't be discussing marriage. I guess what I'm saying is that it all depends on the people involved in the relationship, as with any form of relationship. I had an ex-boyfriend of many years that was a few months older than me, even though we were almost the same age, we were NOT at the same maturity level. It was a train wreck, actually.
Anyways! I think it all depends on the people involved. Love is love!
..Unless you're 51 marrying a 16 year old. That's pushing it!