I had my ACL done two years ago this January. I played my last season in college football inj free 9 mos later. I was in the gym four days later! I was doing upper body only obviously. My advise is that you can lift uppper body as soon as you are mobile enough to do so. I lifted on crches for a few weeks. As far as legs, your Doc will give you a rehab protocal, and you should follow, and do all your phys therapy.
Only Bad news,
My legs are only now getting back to the same size, but after about six months you will only one who notices. email or pm me any questions bro