My observation is that the population groups are different between young and old workers.
It's not that individual older workers are more productive in any way, but rather that the young cohort contains all the people who will become drunks, drug users, who bring their sex problems to works, who steal and so on.
The young people who are not fucked up are often amazing, but the worthless ones cause more problems and bring others down, so on the average productivity is damaged.
The worthless old ones who have jobs have mastered the art of invisibility, so less often screw things up because they don't do anything. Nor do they spend time inflicting their personal problems/neuroses on others, or perhaps they are easier to rebuff.
FWIW, I'm past the 3/4 century mark. That's my credential.