thing,
At the very top, age is not really the issue. It's lower down the 'stars' that one is more vulnerable and it has now become a situation that after - say - an appointment at 1 or 2 star, if you can't be appointed to another job, you will be required to leave. There is also much inter-service competition for joint/combined service posts. I know of a one star and two 2 stars who had to leave despite being exceptionally gifted.
The interesting thing is: who will be VCDS vice Sir Stuart?
Old Duffer