A colleague currently attending an industrial relations conference in Bangkok wrote, "Japan has a very interesting model to handle Greying Issues and the re-employment of senior workers. The retirement age in Japan is 60. When a manager retires today, he is being re-employed as a consultant and plays an active role in guiding his deputy who is promoted to take his place. This excellent solution provides both good career advancement opportunities to younger colleagues and re-employment opportunities to more senior colleagues, where their much valued experience can be shared and continued."
I prefer another model.
Not too long ago, a senior person stepped down from heading an organisation in Singapore. He continued to come back to the office afterwards. The new man sent him a memo to such effect; requesting him to vacate the office expediently, as his continued presence was not helping the transition to new leadership.
The old man's office was moved out of the premises soon after. And he has gone on to contribute to other organisations in other ways.
When a manager retires, he should let the new man handle his job without his looming presence. This will enable the new man to pursue his ideas freely without any shadow lurking around.
This is especially useful in situations where one's predecessor is what Harvard Business Review describes as a "narcissistic leader".
Separately, it is useful in roles where your position requires absolute independence. For example, as chief justice of a country.
The old man is, of course, free to share his experience with other companies. The world can be the old man's oyster.
After all, a good manager's expertise is transferable skill and can be as valuable elsewhere.