There was a similar age gap between my grandparents and they were happily married for over 40 years. On the flip side, I'm not even 30 yet and one of my friends was married and divorced in the space of 4 years to a person just a couple of years younger. Age clearly doesn't equate to remaining happily married until death do us part.
In my opinion, you love who you love and that spans across lots of years. There's too little love in this world these days to start discriminating about who qualifies to end up with who. Just let them be happy together!