As with any pastoral position, the main requirement is that you have a recognized call on your life. Beyond that, here's a few things that can help.
1. Talk with your local church. If you dont' have a local church, get a local church. Find out what the requirements are. Your church or denomination might have their own requirements.
2. Become a youth "leader". That means, help out with the youth group (officially). Start to train with a youth pastor, as a youth leader. This will help you to see the call on your life.
3. A college degree isn't required, but is very helpful. If you don't already have a degree get a bachelor's degree. This can be in any subject, and is probably better in a non-theology (Bible) degree. It is good to get well rounded education, and you will get your Bible training in #4.
4. Go to seminary and get a masters degree. A master of divinity is only different from an MA in that you do Biblical languages. While you probably won't need much Greek and Hebrew as a youth pastor, it is good to have the MDiv degree in case you are called to another position in the church later on. It is important to get the masters degree as most Bible College bachelor's degrees aren't worth much in the American Church's view. You might already be a youth pastor by the time you start seminary...that's good. But you should work on the degree even if it takes you 10 years. It is good to have the theological background and most seminaries are also good in practical application now a days.
If you do it this way, it takes a while but all the doors will be open to you. If you are content being a youth pastor of 10 kids at a small church, you don't need to worry about all this (although it can't hurt). If you want the doors open so you can use your giftings to the max, this is the best way.
Let me know if I can help out in any other way. God bless you.