<p>I plan to join the USMC Infantry reserve when i turn 18, and possibly pursue commission when i graduate at 20. would being military help me get accepted to some 4 year schools? or will it have no effect at all? I want to be an Infantry Officer in the reserves and hold a good full time job (im considering Law Enforcement or going to Law School/Medschool, subject to change obviously) when i graduate with a BA in Political Science/Psychology (also subject to change).</p>
Military training can impact your admissions application. This depend on your purpose and goals. Will it hurt? Definitely not. Will it help? It depends on you sell it. Since you’re pursuing a Political Science degree, this will help tremendously. Tell the college you want real hard experience by joining the military.
If you decide to join the USMC Reserves, I highly suggest you look into the Reserve Commissioning programs the USMC offers. It’s worth looking into, and not many marines apply. If anything, in this downsize, less Marine officers are commissioning in the drawdown. The USMC is looking for officers in the reserves. Not many want to switch over since the active duty officers want to retire and the attrittion rate in officer school is high.
I suggest you start working on your pullups though 
Hope that helps.