We have discussed this topic.
Originally when we were in our 20s, we thought, "We are done when we hit 40."
Why we put a fucking expiration date on it, I have no idea. It made no sense.
Then we came to a realization. Our exit from the lifestyle does not mean that it is OUR exit. One can exit, one can stay. I do not own my wife, nor does she own me. If jealousy were an issue, why are we in the lifestyle in the first place?
Our conclusion was simple: We will continue to be in the lifestyle as long as our genitals work. Once they are done, that person is done. If the other's works, woo hoo, go go go! Go get some! We are on this spinning rock for such a short period of time. To restrict the one you love from enjoying that time on the rock seems so selfish to us.