We seem to be talking past one another. Consider first, that Christian discipleship is a lifelong calling, and that it is a calling for all believers, not just those who are led into special roles, like pastoring. So one ought never to retire from that.
But consider, also, that as our churches have evolved, they have learned to make it possible for those whose services were needed full-time to earn a living from that work -- not to gain wealth, but to earn a decent living. And that in turn makes it possible for pastors to discern the right moment to retire from full-time employment and follow other dreams as well.
I have seen too often the phenomenon of pastors preaching and serving a church well past the capacity to do so, simply because no one had invested in a retirement program for them. One of my students (from my campus ministry days) was called to a church where the pastor was able to do nothing more than be driven to the church building on Sunday morning, was carried in to the service, and preached from his chair. The messages may have been wonderful, but the behind-the-scenes work of pastoral care, administration, education, etc., all deterioriated, and when the old man died, and the church called my student, he found he had to rebuild everything from a crumbling building to a non-functioning organizational structure. It did not have to have happened that way.
As for me, I served as a full-time pastor until I was 66, but sensed not only my energy waning, but also some decline in the church's vigor (i.e., attendance, giving, and new member acquisition slowing down). It felt like the Lord's signal that it was time to step aside and let there be someone else to build on what I had done. And, beautifully, even before I had left that pastorate, there were opportunities to serve as a Foundation executive and to teach on an adjunct basis at a seminary. I am feeling that God's timing is the right timing, and when we sense it and follow it, new opportunities for ministry will indeed come our way for as long as we are able to accept them.
Oh, and then there is the ministry of supply preaching ... gotta go, I'm filling the pulpit tomorrow for a pastor who has had surgery! I love preaching here and there, observing what is happening in our churches, and learning how I might help with some of the issues I see there.