If you both are at similar points in life or have the same mindset, age doesn’t matter.  Also, it should be legal.

I feel that the only time age plays a role in a relationship is when either one person is too immature to handle a relationship and the other is mature enough to realize that, or when one person is at a stage when they want to settle down while the other one is still not ready to.

Besides those three things, I think age doesn’t matter too much.  It could be a day, it could be 20 years.  As long as both people are understanding and mature and willing enough to work through whatever problems may arise, it matters not.