My dad was a Marine, and when I was younger, I wanted to join. However, a back injury playing football in 10th grade, and a serious motorcycle accident took care of those plans..
I have had a good life, and been very fortunate in many things, but there will always be one thing lacking. I'm almost 50 years old and can't change it, but I still have the desire. You can always look back afterwards and think, that really wasn't what I thought it would be, but you will always have a huge sense of pride and accomplishment. Thats better than looking back saying, I sure wish I had tried.
My best friends cousin joined the Corp when he was 18. He came from a bad homelife (abusive drunk father) and just wanted a way out. He retired from the Marines last year after over 25 years of service.
We were all your age at one time, and there are a lot of decisions to make. It can seem overwhelming, but it will work out. My son is 14, so we are not far from going through that with him.
As a parent, we all want the best for our kids, and don't like the thought of them going of to war and being being injured or killed, but we also respect their wishes and desires, and even if we don't agree with them, we will always be supportive in their decisions.