Yeah, I completely agree that someone who is 18-20 just doesn't have the life experience to know a lot about relationships in general.
My wife dated a guy who was in his mid-40s when she was 18 and, with hindsight, it seems like her inexperience with life, intimacy, and relationships was actually something he was looking for (gross).
I guess I assumed that the person OP likes is at least in their mid-20s. I mostly added the legal adult part to cover my ass in case a snarky commenter was like, "oh what if she's 16?" trying to be smart.