Connor/Cordelia: Age Gap?

I'm stilling rewatching AtS season four, finished Awakening. Here's something I don't understand: why do people keeping making comments as if Cordelia is so much older than Connor? If she's Buffy's age, she's 21-22 to Connor's 18. That's only three or four years. Connor/Cordelia is squicky because she used to change his diapers and has a thing for his dad, but there isn't match of an age gap there.