Odds of Getting In
Just like every other artistic field, fashion photography is as hard to get into as one of those products wrapped in impenetrable plastic. You know the kind we're talking about? It's like you see the thing you want in that shiny, plastic shell, but then you need hardcore scissors to open it. But then you can't find your scissors, and when you do they're too dull. So you find your dad's old box cutter, and then you end up in the emergency room getting stitches because you nearly cut off your thumb.
Yeah, breaking into fashion photography is pretty much exactly like that.
If you're determined to take a swing at it, though, a good way to start is to become an assistant to a professional. Hopefully, your new mentor will be cool. They'll show you the ropes in between the times you're fetching their breakfast sashimi every morning. Of course, your mentor could also be a narcissistic maniac who'll make you regret the day you were born, but you'll have to suck it up. You need this shot.
You also need to use your time as an assistant to do some major networking. Afraid of being schmoozy? Too bad. Be schmoozy. You're going to need those contacts if you ever want to have a chance to go out on your own. By the end of your assistantship, you need to have accumulated a portfolio (on your website and a hard copy) that will wow every photo editor or gallery owner out there. There are thousands of people out there trying to do the exact same thing as you, and if you want to have any kind of shot you have to be better.