This is not terribly surprising if you think about it, 18 is the point where girls get fully out of the awkward puberty stage and get legit hot.
My already mediocre age-judging skills go straight into the crapper when it comes to females from about sixteen to the early twenties, I think the 18 thing might be sour grapes, men conditioning themselves to think that if someone is younger than 18 they aren't hot, to avoid getting themselves into trouble.
Men are easier to tell the ages of, at least, if they wear facial hair.
Jell-o, I think zero might have a point, even if you don't find girls, you do have mount hood to go up on whenever you feel like it, and it rains a lot.