Starting Exercise After Surgery

I am scheduled for surgery on June 12th and just wondering how soon after surgery will I be able to start exercising.  I know that walking is encouraged, but how about going to the gym?

I started walking right away.  I would say that I was walking hard at about 3 or 4 weeks.  I morphed into running a 5K in about 5 months.  As far as lifting, I waited 6 weeks and started really light.  It felt like too much so I waited another 2 weeks.  It turns out that I should have waited more because I ended up with a hernia.  It's not too bad though. I would wait 6 weeks to do anything even mildly strenuous.  If it doesn't feel right, it isn't