Yeah, I've heard that one, too. What do I think? I think that love and math have very little to do with each other. What if you fall in love with someone outside that range? And who came up with that equation, anyway? I don't think it was Pythagoras.
I say date who you want to date regardless of age (as long as it's legal, of course). I do think that like any significant difference between two people--race, nationality, religion, etc.--a big age gap can bring its own set of challenges to the relationship. The less you have in common, but more difficult it can be. But then, all relationships have challenges, so don't let that stop you from dating the person who makes you happy.
Thanks for the question.