In European academia there is a mandatory retirement age: if a university professor becomes older than 65-68 years (depending on country), he cannot hold a position anymore. This was also the case in the US some 30 years ago, when the Age Discrimination in Employment Act still allowed for the mandatory dismissal of tenured workers.
A few days ago I was told a fascinating story of John Bennett Fenn. He was working at Yale for a quarter of a century, until he reached the mandatory retirement age of 70 in 1987. After a while, the law was changed to fight the age discrimination, and Fenn became officially allowed to get a job. By that time his ex-position at Yale was still vacant, and he applied for it. Believe you or not, he didn't get it.
Eventually Fenn joined Virginia Commonwealth University in 1994, where he started working on the Electrospray ionization technique, for which he shared the Nobel Prize in 2002. John Fenn was 85 by that time and he still remains the oldest Nobel Laureate in Chemistry.
Yale University claimed that Fenn was working on electrospray ionization while still holding a position there. After submitting a lawsuit against Fenn, Yale was awarded over one million dollars and partial patent rights to the technique.