Kid you have PLENTY of time before you even need to think about joining the military. Your 14. Enjoy it while you can. Girlfriend?? Serious?? Trust me when I say at 14 a guy has NO IDEA what being serious about a girl is all about. If it's getting serious to the point of having sex, you better wrap that thing up. Last thing you want is a kid. Better yet just keep it in your own pants then you wont have to worry about it.
When your older and ready to get out of school, that's the time to start looking at the military if that's what you really want to do. If you want to be in the military and have some money to go with the job, get on the ball, get your grades up in ALL your classes and try to go to a military accademy or through an OCS course and be an officer.
As far as the different branches, well they all have their own flavor. I've been fortunate in my life and military career to have worked with ALL of them. I did 4 years in the Army and then finished my career in the Coast Guard. I grew up on Air Force bases and have been stationed next door to the Navy and Marines.
Air Force=Plush living, the BEST bases, but unless your a pilot you will ALWAYS be a second class citizen. The Zoomies get all the glory while everyone else does 99% of the work.
Army=Bullet Catcher. If you don't mind living out in the mud, heat, cold, rain, snow and what ever else mother nature can throw at you, then it might be for you. Plan on moving into position, dig a fox hole and then 30 minutes later get ready to leave to only do it all over again in 4 hours when you get to your new position. There are really only 3 class of people in the Army that matter. Infantrymen, Artillerymen, and Armor/Calverymen. Those are the combat arms that get it done. Everyone else just supports them i.e. second class citizens.
Marines=PROFESIONAL Bullet Catcher (every Marine is a riflemen). Just like the Army but with the added benifit of getting to deploy on Navy ships for 6 months at a time.
Navy=Never Again Volunter Yourself. I honestly could never recomend the Navy to anyone. Been on their ships and living on one sucks. Cramped quarters, gone all the time, and for the most part all they do is turn circles out in the water, unless your on a carrier, then you bust your butt for 14 hours a day just so you can climb into a rack/bed the size of a coffin. Plus they have ugly uniforms. I mean really....who wants to wear a dixie cup hat????
Coast Guard=Well I'll admit I'm biased towards the Guard. I loved the time I spent with them. It's small but we do everything. The only branch of service that conducts law enforcement operations on a daily basis. It's also the only branch that gives commands to enlisted personel. My first ship USCGC Scioto which is a river buoy tender was commanded by a Chief Bosn Mate (E7) 13 man crew and was the BEST command I ever served at. Anyway the Coast Guard can let you do all sorts of thing. Myself as an excample: My rate in the Guard was an Electronics Technician. I worked on comms gear, navigation gear, tacitcal computer systems. That was my "full" time job. I was also a boarding team member, small boat cox'n, combat information center watchstander, .50cal gunner, flight deck crewman, buoy deck supervisor, intel petty officer, and had a ton of other little special projects tossed my way that I was in charge of. Coast Guard places alot of responsiblity on it's junior and senior enlisted people. It's not uncommon for a third class petty officer to be placed in command of a 41ft patrol boat and sent out to conduct law enforcement boardings all on their own. These are 19-20-21 year old kids being given command of their own boat and being trusted to go out and do the job unsupervised. Try finding that in the other branches of service.
Do your research when you get closer to being able to enlist but make an informed decision. There is more to "serving" your country than getting shot at in a war or killing the enemy. If you want to join the Marines right now because you want to be a badass, your looking to join for the wrong reason. If you have a girlfriend that can't support your decision to serve, ditch her quick. There should only EVER be two women in your life who's opinion you should listen to conserning MAJOR decisions. Your mother always, and your wife if she has a functioning brain cell in her head. Girlfriends have no say over your life except for the immediate situation. Like where your taking her to dinner, and she gets to decide what movie your going to see, but that's about the extent of it.