Hi Kathy,
Knowing that everybody's mileage varies anyway and that there is only one way to find out for sure, I'd suggest to just give it a try and see if you are comfortable. I don't think there are any concerns since you are already 4 years post-op and should be fully healed up. Also, after the first ride past a longer break a bike's saddle usually hurts under the pelvic bones and not on the genitals, so I think that shouldn't be a problem either. If you have access to a stationary bike, for example at a gym, give it a try there first before investing any money. Even if your old bike is not ready for a ride, you could at least climb on it and see if you are comfortable sitting on the saddle for a while.