My 1st husband was 15 years older than me and we were married for 21 years. My 2nd husband is 8 1/2 years younger than I am and we have been together 6 1/2 years. It is what ever you are comfortable with.
i don't think age should be a factor as to whom you want to marry.
My parents have an 11 year difference and me and my wife have a 3 year different.
so i beleive age is nothing but a number, and the main factor is love.