I agree quite strongly with the issues raised here. Age is not just a number. It's very important to consider that people want and need different things at different stages of their life, and often a large age gap can make those things incompatible. It's nice to think that love conquers all, but if you're twenty and your man is forty, what happens when you start to want children?
What happens to the children who were born when their father is fifty and so have a sixty-eight year old man as a father by the time they're eighteen? Not everyone can maintain a healthy lifestyle, so you have to face the fact that these children might see their father die young. You also have to consider if at fifty you're prepared to potentially be taking care of a seventy year old.
I'm not saying by any means that people shouldn't be with someone much older than them - indeed I've seen it work very well with some couples. But you need to be honest with yourself and with each other about what you need, and what the other half can provide.