I spent almost 9 years in the corps. I turned 18 two weeks before graduating from MCRD-SanDiego over 30 years ago. Two 4yr enlistments plus an extension during my first enlistment (for an advanced school). Worked with special units for many years and was in the field with Army Rangers, Navy Seals, spooks, and flown around by Navy and Air Force.
Both of my boys joined the Army. They both said my stories of boot camp and some of the missions that I went on scared them out of the Marine Corps. The oldest is an Army Tanker (was part of 4th ID but they have been changing things up the past year), he is on his second enlistment. The youngest joined and then went to Ranger School. Graduated and on his first training exercise with his new unit he was injured, had shoulder surgery, and was then put out on medical.
The main thing is that the military will make you grow up quickly. If you join up, then stay positive. There is nothing worse that being negative about everything. I enjoyed every base I was stationed at, thought a lot of others did not. I was in some hairy spots and our units took casualties, but overall, I would do it all over again if I could. Comradery, support, friendships, thrills, some I miss, some I don't.