Welcome to the site, Woodstock! I understand your concern, I think we've all been there with the pain.
My progression was pretty quick between just being sore after working out, and pain walking. I let it go to dislocating one hip before I knew it was time to check it out. Everyone progresses differently, and as Jeremy notes, it may be affected by different things. I was very active athletically, and that probably prolongued it in some regards, but it also led me to ignore what was happening.
Five years before the surgery, I had an ultrasound and was told that my cartilage was slightly down in one hip, and perfect in the other. I was told I had at least 10 years before I needed anything. Three years later, I was limping everywhere and although still playing a lot of sports, it was through pain. Two years before the surgery was the first dislocation, then they became more frequent to the point of happening while sleeping. The XRay done then showed no cartilage on one hip and almost none on the other.
I don't think anything happens gradually, I think it follows chaos theory more, being in one plateau, then going fast. You seem to be reaching the point of decision, and that time will be all yours, all of us reached it one way or another.
The encouraging thing is that this procedure (done twice on me last year) has really worked on me and others on this site. Make sure you pick the best surgeon possible, which may not be who is treating you now. Interview surgeons, and use the recommendations here as one input - the final decision is whoever you feel good with.
Good luck and keep in touch. There are many good and supportive people here, and we've all been where you are.