Being only a few years older than you, I would suggest completing school.
I'm not sure about America, but if you want to be an Officer in Australia you must have passes in four grade tweleve subjects to be viable for entry. It is always good, however, to show that you have completed your schooling no matter the job.
Another point I would like to rise is that you have no former experience and are simply just jumping into mostly SF units such as Rangers and SEALS. Perhaps it would be beneficial to try another job and work your way up to SF level. That way you have more experience. Being thrust into an extremley hardcore enviornment at such a young age could be physically and mentally destroying. Therefore I suggest working your way up the ladder to SF. By the time you get there, you'll have a good understanding of what it is like to be a soldier, how mentaly and physcially taxing it is to be in such a job, and you will have a better understanding of yourself as a person.
Cheers and goodluck,
TangoWhiskey.