Hi andrew.
First of all, with very little knowlege on Navy SEALS, I would bet that they do have 50 cal SWS(Sniper Weapon Systems) of this kind or another. But at your young age I would advise you to think more about what you need to do to be in the military in general, not such a very specific unit let alone very specific role.
The things that you need to do(in my very hones opinion) are:
1)Study hard and get good grades. If and when you will try to be a sniper in any unit you will need your math skills for sure.
2)Go to what ever youth military group you have at your scool/area.
3)Start getting in physical shape. I dont know what shape you are in now, but do it gradually(you have at least 5 years before joining, no rush).
4) Seeing as you are lucky enough to live in a great country that gives you options to train with firearms, look for these options. If your dad, mom or whatever adult relative own a rifle of some sort(I assume they do if you live in Montana), ask them to go shooting with them as much as possible.
5) Develop self-discipline. Dont over sleep, over eat, get use to being polite(even to people who dont really deserve it), listen to people carefully. All of this skills will help you become a very good soldier when and if the time comes.
All of these things or just one of them will help you alot, as far as I know. The American members here might have diffrent ideas.
And remember its not really that important if you area Navy SEAL, Tank driver, Military Police, what ever. The most important thing is doing your job to the highest possible standart and serving your country.
