Kerunai,
They won't card you when they deliver it...they used to ship it RPS which I think is now Fedex ground. The boxes do have stickers on them that say "non-flammable gas", so if you've got parents around that may raise a few eyebrows. I've only found one place to do this on the net, but I'm sure there's a few others. BTW the lab grade and the medical grade are almost exactly the same purity, but you can't get the medical stuff without a license. If you're lucky enough to find this place, just put "labs" at the end of your name or make up something that sounds legit, although I don't think the guy really cares. Also a word of caution that probably everyone already knows-if you get a tank ALWAYS fill a balloon first and NEVER put your mouth on the tank. The stuff is VERY cold coming out and if you accidentally turn the valve to much you can-put simply-blow up your lung(s).