Well regardless you have at least four years before you can legally join any branch of service. During that time I think you should determine why exactly you want to join. "To protect my country" is okay but it is kind of ambiguous. Just be aware that the military is absolutely not what is portrayed in Call of Duty or any other game (you think I am joking about this but I know guys who have enlisted and claimed that they did so because they loved Modern Warfare #1). It requires complete dedication and personal-investment in training time and physical fitness.
That being said, first you should go to college. If you want to enlist, there are promotion bonuses that come with college credit hours (i.e. 48 credit hours = automatic promotion in the Army to Specialist upon enlistment, etc.) and you will put yourself ahead of your peers who enlist straight out of high school. Also, you have the option of doing ROTC wherein you train as a cadet for at least two years of college while taking regular college classes simultaneously. Upon graduation, you are commissioned in the grade of Second Lieutenant and head off to training right away. As an officer you will be given more responsibility than enlisted soldiers, but you will also enjoy a higher salary and respect.
Also, I disagree that Infantry is a poor man's job (yes Comr4de, I know you're joking). It is true that Infantry is exposed to a more physically rigorous lifestyle than some of the other branches, but it is also at the forefront of combat. Wars cannot be won with tanks, bombers, fighters, or ships. Wars are won with infantry to occupy the ground and take the fight to the enemy's doorstep. They are also paid on the same scale as all other branches.
As for the other branches of service (Air Force, Navy, Coast Guard), they are respectable and serve an important purpose in today's operating environment. They, however, don't have much of a mission at the moment. There is no longer the need for stealth bombing operations or aircraft carrier battle groups. The current state of conflict is on the ground, carried out by the Army and Marines. If you want to join either the USAF, USN, or USCG you will be employed and will be relatively safe, but you may not see the kind of deployment that you will with the Army and Marines.
There are many options that you can choose from. The only perspective I can give you is that of the Army. Obviously I could talk forever about this so if you have questions feel free to ask.
