I haven't personally got experience (I should be so lucky to get a toyboy) but look at Joan Collins, her husband is 30 odd years younger than her! Juliet Mills is married to Maxwell Caulfield who is 18 years younger, Demi Moore is married to Ashton Kutcher who is 15 years younger, Madonna is 9 years older than Guy Ritchie...
You see what I'm getting at? Lots of women marry younger men - I know all my examples are famous but many ordinary women do it too.
You've been together 10 years already so you must have a solid relationship, forget his age, do you want to marry him? If you do then go for it! Age is just a number after all...