As already mentioned, you'll need time for your body to heal after surgery and for your pouch (and you) to adjust.
That being said, I was an exerciser before j pouch surgery and continued after surgery. (I am not an athlete by any stretch for the imagination. I am a power walker in warmer weather, and use a recumbent bike inside this winter. I don't run, not because of my pouch, but because I'm not a runner.) Needless to say, start slow with walking or using an exercise machine in the house. (I did this to be near the bathroom in case I had to go in a hurry.) After I felt I was doing okay in the house with exercise, I expanded to short walks outside where there were places I knew I could stop and use the bathroom if needed. This helped me build up strength and endurance. I continued to build up from there.
I'm fourteen years from my surgery. I now walk four miles outside or ride my recumbent for an hour. I don't usually have to use the bathroom unless I didn't go before I started, or drank way too much water before heading out. You will not need to wait fourteen years to get back into the swing of things
Start slow doing what you love and remember you're headed for the long haul. Don't try to get back into everything right away, but also don't be afraid to get out there and try. Get some people around you who understand your situation and understand if in the beginning you need to use the bathroom more. No, you're not going to be doing this right after surgery, and maybe not anything heavy for the first year, but as you gradually build up strength again, you'll know more what will and what won't work for you.
Wishing you the very best!