Kevin was a necessary plot device, for Terry always being in danger of being 'found out'.
Whose idea was it for the word "Lisp" to have an "S" in it?

It might be that Terry and Kevin were dating when Kevin was a senior and Terry was a junior.
Then again, Kevin seemed older than a college freshman, more like the age of someone who already graduated.

In almost 80's movie (and in real life back then) the high school girl had to have a college boyfriend. Secret Admirer, Can't Buy Me Love, Fast Times, etc. My advice for Kevin would be.if you need someone more mature and serious, maybe try dating college girls! If you're no longer living at home, it might cramp your style to have a main squeeze with a curfew. Just a thought.