Age difference between your significant other

Me and my fiance are 13 years apart, he worries alot about me leaving him as he gets older, I don't fear because I feel our connection Is stronger than physical attraction. We have been in each others lives for 6 years and our connection has never faded in the slightest. Does anyone else have an age gape or have a significant other worry like this? I try to calm him and reassure but it still concerns him because he has seen friends with an age gape and they have been left, heart broken and alone. :/ I don't worry about age gape much I know he will age faster and I accept the responsibility of caring for him as he has cared for me for so many years. Opinions?