how old is too old?

when you get into the dating stage as a teen (14/15) sometimes you find someone your age attractive and Sometimes you find someone 17 or 18 attractive. so how old is too old? There always has been that saying going into highschool, "that senior doesn't really love you" Is it always true? Or can you find love within a 3 year age Gap? Do you have any advice on dating? Perhaps high school love stories of your own? I'd like all the advice & understanding I can get 😊