There are really only two reasons a labour leader does not retire by 65. They are either so arrogant that they think no one else can do their job, or they have not done the work needed to prepare the next generation to take over.
The third reason that is missed is that the leader cannot afford to retire.
The basic premise, that failure for older workers to leave the workforce results in the inability for younger workers to move up in the workforce, is basically sound (ignoring the whole "create your own position" possibilities that most workers won't do anyway).
There are only so many senior roles in any given organization, and only so many middle management roles, and only so many front-line management, and only so many senior workers, and only so many intermediate level workers, etc.... the number of any given position in any given organization is finite. If the upper management never leaves, no one can replace them. You're not getting 10 CEOs just because none of them feel like retiring. A department won't have 6 different directors in charge of the same things and same people. I don't know that suggesting people should retire by 65 would count as "early" though, since most worker (in the US anyway) retire earlier than that in reality.