12-18 months sounds like a long time. i thought allografts were supposed to allow for faster rehab, since you aren't also having to rehab whatever tissue they took to make your new ACL. maybe, when it is a second reconstruction, they want you to take it more slowly.
stallworth's down time shouldn't be so long. when i had my first ACL (7 years ago), i was cleared to do whatever i wanted after 6 months, and after 12 months i didn't need the brace. of course, i wasn't playing D1 tackle football. i had my second one three years ago. two different doctors said it was just bad luck - the second one was supposed to be stronger than the first. well, now i'm on ACL #3. no more sports with cleats for me, just basketball and softball with turf shoes. and i'm still wearing my big expensive don-joy (like you see OL wear). if i have another one, i'll be using OPT too...
best of luck on your rehab. if i could suggest anything, i'd say go above and beyond on the rehab, and don't stop the exercises when you are released from rehab. </p>