We had a special pioneer in my congregation growing up that had long since stopped meeting the hour requirements for special pioneers, but was allowed to keep the title of special pioneer due to her age. This allowed her to continue to receive a stipend. They also allow long time elderly Bethel workers to stay on at Bethel. In both cases, while not calling it "retirement", it is essentially the same thing and it is an ongoing expense.
I would imagine that elderly COs are given a similar stipend once they hit the max age.