Some doctors do advise limits to lifting after J-pouch surgery, but most encourage unrestricted lifting (after complete healing from surgery). 

I lift and do ab work no problems. Had j POUCH 2012

I was doing heavy squats within months of surgery, but that is not smart.... no injuries occurred but I may have been lucky.  From my experience, given adequate time to heal, there would be no limitations at all.  Everyone is different though.

I've been lifting 1 month post takedown. My surgeon suggested weightlifting after 10 days post surgery but I started only a month after to let the stoma site heal. I lift very heavy for my weight. I am at 125lbs at the moment and I can do 140+lb deadlift or a 120+lb  squat. I've been benching at 110lbs now. There was only once I felt a little pain in my stoma site when I lifted heavy on deadlift without my workout belt and went for dumbell rowing. I am 7 months out from takedown and I was weighing 93lbs just after final surgery. So I'd say go out and just start doing any exercise you want to and dont think of any other thing. I've been hitting gym 6x a week almost for 6months now without a single issue. I do all core and ab workouts too now but only in moderation. Start slow, you'll know when you need to go up higher. 

47 and I lift roughly 5 days a week. Abs, squats, etc, no problem. I have to be strict about form.  My abs don't "flex" the same way at my old ostomy site and I have to be careful to not let that site bulge out.

I had takedown in 2013.  After recovery at least a few months, I did not do  any major physical chores, work or exercise. I introduced my activities back.  About 5 months later I noticed a bump in my stomach it was a Hernia. I was then starting the process of moving and could have out did myself in lifting.  Now 5 yrs later it is larger and I need surgery.  My dr said after this surgery I can do anything I want after the recovery time.  We will see.     I guess it depends on the individual.