I suggest that you find a doctor in sports medicine to work with your surgeon. He/she should be able to evaluate the risks so that you have a better understanding of your choices.
That said, I have a friend (Mr SuperCowboy himself! LOL) who is about our age (yep, I'm in your ballpark) who has a large cutting horse operation, who has had a knee and shoulder replaced, a finger joint, several lumbar vertebrae fused, and too many breaks and tears for me to count. While he no longer works the green horses, he hops right on his proven horses and takes off.
I have had an elbow replaced, and plates, screws, and pins, put in my ankle and tib/fib and am currently working on nerve blocking in my lumbar spine.
My thoughts are that it up to each person the risks they want to take, that at this point in my life I am not looking for that fiesty wild ride, but for something that is fun, reliable, and as safe as you can get in a horse. I plan on riding for as long as I have the energy and the crane to lift me into the saddle.

I am not one of those who in expressing opinions confines themselves to facts. - Mark Twain
The fact that man knows right from wrong proves his intellectual superiority to other creatures; but the fact that he can do wrong proves his moral inferiority to any creature that cannot. - Mark Twain