Each individuals has thier own unique experience in the military. I was in the Air Force for seven years, and I enjoyed it for the most part. I was a great experience, and I learned alot about myself. I wanted to see how far I could push myself, and I wanted to prove to myself that I was tough enough to make it in the military. I wanted to be in the military since I was a kid, but was relunctant at first because I knew that I'd have to go back in the closet. However, there are days where I fell like if I could do basic training all over again, I would.
When I was in basic training, there were guys who were alot larger and more masculine than myself who cried like little babies and they wanted to quit. I had a perma-smile when I went through. The camaraderie amongst your entire flight/unit is awesome. It is one of the best feelings in the world. Basic training is all a mindgame, it's just a matter of whether or not you can play along. As well as pass the physical fitness test of course. Also in Air Force basic training you have to pass a writen test as well so if you're not book smart, I might think twice about it. Also in the Air Force, amongst the enlisted ranks, you have to take a written test in order to get promoted. If you don't like taking test the AF is not the branch for you.
As far as fitness level goes, I'd start right now. The AF rates physical fitness on a sliding point scale. It's based on your age and sex. I'm not what the other branches do, but the size of your waist does affect your score. So for man your age, in order to get a perfect score these are the numbers you are looking at:
Body Composition: abdominal circumferance < 32.5 inches
Aerobic fitness: 1.5 mile run <= 9:36 mins
Push ups: # of reps in 1 min >= 62
Crunches: # of reps in 1 min >= 55
Remember these numbers are what you are looking at if you want a perfect score.
Also, as far as sexuality goes, just be cautious. Some people are much "luckier" than other. As far as my sexuality goes, I've had it much easierthan other. My family is accepting of my sexuality, and we all love each other. I've never been bashed. People tend to like me as a person, and they don't focus on my sexuality. When I joined the military, I thought that my luck would run out, but it didn't. I came out while in, and no one seemed to have a problem. No one forced me to get out, I seperated on my own terms, and I'm happy that I had that opportunity to do so. I think that it part it may be the fact that statistically 1 out of every 5 people in the AF is GLB. That doesn't mean the AF is "gay friendly" because it's not. Anyways, the choice is up to you, and good luck with the path you choose.