I just looked at my Polar Fitness Log and exactly 3 months after my op I must have gone to the gym and did 20 minutes on the treadmill with heart rate near max 153, I'm guessing that I started with incline and moved later back to running. Followed by another 20 minutes of what must have been weight machines. I went about once every couple of weeks and did plenty of walking in between.
In the 2nd month after my op I flew to Australia for a month so there is only walking which seems to be the sensible thing.
Lifting worried me most as the wounds in my stomach definitely didn't like it, so I didn't do it until I felt it was well recovered. Also the sphincter stitching was something I was very careful about but that's another matter.
I didn't ask the doctor it seemed like common sense not to strain anything and to introduce it slowly.