Honestly it would seem pretty shallow to say that they couldn't be an item as they are now.
It's not like they're different ages, by all accounts. Why are looks the deciding factor here? Grandpa Feng is a sweetie, I personally probably would happily date him as-is, if I'd had an old torch for him, even if I had come to look a lot younger than him now.
Well, I get that it might look bad to an undiscerning public and everything, mind.