Well I would be less cautious than Lyn. I should point out I have had RT not surgery, so hardly any chance of me injuring myself as a result of the prostate procedure.
I suspect each extra week you give things to heal the better, so 2-4 weeks almost certainly too early.
Assuming you are not riding as if you are on a race track, the normal stresses of riding a motorcycle may be ok, but when you do something silly like put the side stand on a drain cover which breaks, and you find yourself looking very embarrassed in the supermarket car park with a bike on its side. You are going to want to pick that bike up damn fast, and then you will forget two months ago a surgeon chopped through your abdomen. You will then do a serious injury which will set you back months.
We have had plenty of members who said I was doing great then I did the gardening at the weekend, or just carried all the wife's shopping in, and now I have had severe pain for the last two weeks.
So next weekend I shall really enjoy a nice ride out on Sunday and I'll be thinking about you.๐