I just got to level 8! I thought that I would get a T shirt now but they didn't say anything about it...I need to give them my address.
Check your notifications. When I hit 8, I got a notification that took me to an in-site message about the shirt, and took me to fields where I input my address. Make sure you haven't missed that notification; maybe allow some time to pass for it to hit. If you still don't have it in a couple of days, contact SiteSupport. I hit in early December, I think, and only recently received a PM advising that my shirt will soon be mailed, so they may be running behind on the IRL end of the process. There may be tech issues with the site hampering the process. Membership continues to grow, as I understand, but I don't know if they've added more human beans to put t-shirts in envelopes and print mailing labels and whatnot.