Hi James,
As you're young and somewhat inexperienced with women, you may want to consider allowing yourself to date as many women as possible when you're starting out. I'm not saying to be a player, but get to have as many experiences as you can.
You don't necessarily have to "tell" potential partners that you have a "hair fetish" -- at least not immediately. Assuming you have the opportunity to be intimate with them, let them know how much you like their hair. Tell her how silky it is, how great it feels against your face or your chest. See how she responds and see where it goes. When you find someone who you feel you may be compatible with, and who responds well to your your lust for her hair, then you might use the word "fetish" in talking about it.
The problem with using the word "fetish" with a partner -- especially one who may be a little jealous -- is that once she knows you have a hair fetish, she's going to be watching how you look at other women's hair. And sometimes that can be a recipe for trouble. Assuming she's someone you're planning to be with long-term, keep it to having a thing for *her hair*.
Best of luck to you -- I hope you'll let us know how it goes when you get into the field!