I'm in the DEP and graduate from high school in 5 months. What can I do to prepare for basic training and 17C school?

Get your cardio up (i.e. run and do pull ups/ push ups instead of straight weight room) start distancing yourself from your friends A to stay out of trouble B you are about to leave them behind to essentially start a new life...don't go to boot camp with a girlfriend...just don't

For starters, graduate. Next, give up any bad habits you might have. You're going to be without access to tobacco for a couple months, so you might as well start now. If you're not 18 yet, don't run out and get tattooed up on your 18th birthday. I can't count the times I've had to tell someone their tattoo is out of regulations. Stay in shape. Eat healthy. If you're on the heavier side, try not to be as heavy in 5 months. If you have friends that like to smoke weed or other stuff, drop them now. You don't want to get all the way to MEPS and then get sent back home because you popped on the piss test.

Good luck and have fun.

Lots of people addressed the physical preparedness so I won't other than to say hit the gym, run outdoors, especially with a backpack with some weight, etc. I'll address the preparing for 17C school as I'll assume you're already accepted with a school date on your contract in the DEP. The more you are prepared the better you'll do, though they'll teach you as much as they can. It is mostly a matter of how much material they're going to try to cram into your head it is like drinking from a fire hydrant. Learn Python, shell scripting, powershell, network fundamentals, subnetting, routing and switching, sysinternals, Unix, Active Directory, ports and protocols, and you should do better than your peers.