If you and the girl are both at similar "mature" stage in life, then it will work out no matter what.
Obviously a grandma who is ready to die should not marry some dude who just moved out from his parents. Neither should a guy who has completely settled, owned his business, home, etc should settle with an immature 21 year old girl. Oh, I hear all these old guys flaming this late 20s guy right now. Trust me on this, you're her daddy and not her equal. If you want to be someone's daddy or son, go ahead. I want someone equal on my terms and that to me makes me more mature than the old dude jostling for some teenage honey.