I have witnessed many of the long-time COs leaving the traveling work. As people age there will naturally be more health issues. In the US, the WTS (HQ or the Circuit) are faced with paying for the healthcare of these fulltime servants. Thus, if they happen to have any kind of serious illness that is causing great expense to the Organization, they will likely be required to leave the traveling work. If they can make it age 65, then they will qualify for free Govt healthcare (Medicare) and as long as they can take the weekly grind required, may be allowed to continue.
However, all of our recent COs have been young, new "company men" who lack much experience in life. They've been to WT Schools for COs/DOs and they know the WTS rules. They've thoroughly studied the Shepherd the Flock Book, but are only average on their knowledge of the Bible. Don't expect them to be able to answer any of the "difficult" questions with anything more than "wait on Jehovah". Most come up short of life experience and for sure they lack any formal education that would qualify them for any real counseling of people dealing with critical issues in life. The old loving, empathetic, granddad CO seems to be non-existent anymore.
They require management who fit their current business model and are "low maintenance".
Doc