It's possible. You can't really count anything out. Quite a few September selectees have been getting March OCS dates, however. MEPS is a big step, but I think the security clearance is what generally hangs people up.
You also have to take into account fiscal years. You may have been selected for FY12, in which case the earliest you could start is June. There's also the possibility they give you a date very far out, only to change it to one earlier.
My processor was concerned about me getting to MEPS 2 weeks prior to the 17th. I'm not sure if it's just because he wanted it all finished before the holidays, or if there was a significance with that date (e.g. they'd be working on a batch of FS letters for that date). I'm hoping that the fact that I'm done with MEPS and have previously held a TS/SCI that I'll get a final select letter before the end of January. If not though, I'm still not done with school until May, so no biggie.