First, it depends on the situation. I'm 36 and have been attending games since I was 6 and have spent a lot of my money on the Sox since I was old enough to work and buy my own tix. I'm taking a year off, does that make me a fairweather fan?
Second, a lot of you guys on here are a lot younger. I wonder how'll you'd feel after 30+ years of losing baseball and different personal monetary responsibilities. I was 21 once too and remember spending every extra dime on Sox games. I've been where you've been, you haven't been where I am.
Last, the word 'Fan' comes from fanatic. If you're gonna split hairs on definitions and labels, I bet very, very few of us are even 'fans'.