Marius is right, it depends on the type of graft you have. As far as I know there are three different grafts. There are the cadaver, hamstring, and patella tendon grafts. The first two are easier to recover from but the grafts aren't supposed to be "as good". The last graft, which is what I had, is supposed to be the hardest one to recover from but is the stronger graft. The first two grafts are done more arthroscopically and that's why you can recover faster. The last one is more invasive and thus harder to recover from.
One thing my doctor told me is to be real careful at around the 3 month period. That is when you start to feel really good and feel like doing a lot more intense activities. But be careful because the graft itself has not fully healed.
Just follow doctors orders and you will be fine. Oh yeah, I had mine done almost eight years ago and almost play exclusively on hard courts and I do fine. I'm 35 by the way.
Good luck. Keep us updated.