Last time I checked Americans are preparing to leave, but it isn't just a matter of "ok pack your bags and hop on the bird out of here." You have to inventory bases, transfer the authority, move units from smaller COPS to larger FOBS, and arrange for local forces to take over security. Heck, we TOA FOB Apache within this month, which is a rather large FOB in RC-S.
*Unless you want to just JDAM the bases all at once and call it good.
Edit: Posted a bit early. The fact is I don't think it's truly feasible to simply pull out before 2014 or at the end of this year. That would give 4th ID in the South, and 101st in the East 6 months to close all remaining COPS and FOBS, remove all firing assets (mortars, artillery) and Fighter Jets from KAF and BAF. Not include packing tricons and transporting them to Kuwait, along with gathering the cargo flights to remove any MAXPRO or MRAP that need to return home or Bradley's for that matter. While, I don't think it's impossible to get all this done in 6 months, I think unless you're willing to scorch Earth the process, it won't happen.
Glossary:
TOA: Transfer of Authoriy
KAF: Kandahar Airfield
BAF: Bagram Airfield
FOB: Forward operation base
COP: Combat outpost
RC-S/E: Regional Command - South/East
MAXPRO/MRAP-Large military patrol vehicles.
JDAM: Joint direct attack munition (GBU - 31)