As long as you are 18 with ID to prove it and have the money, they dont care if you have an ASC account (you might want to mention it as some give discounts). I would also suggest ICS, but at very least make your first gun an M4 or similar (get a rifle not a SMG). SMGs (MP5) are great but not recommend as a first gun. I would say stay away from the SMG for now get yourself a nice rifle (AEG dont get GBBR for first gun), learn your gun, learn the parts, how it works, how to take it apart, the terms people use. Once you are comfortable and have your feet wet you can start building your collection or change to something else. As stated above ICS is proprietary and can be hard to find (battery), however it works well out of the box, no mods or dicking around just toss in your proprietary battery and start shooting.
ICS M4A1, VFC SCAR-L, KJW 1911A1, KWA USP COMPACT