In the end, money is a fiction. It's all about allocating the benefits from current production.
Social security schemes and government-guaranteed pensions mean that the government (=the voters) decides how much each currently productive worker has to give away, and how much each retiree gets.
Private retirement funds mean that for each retiree, the amount of money earned from their own former productivity which they relinquished into their retirements fund AND the amount of money they acquired otherwise and put there AND the management of the fund AND other economical factors influencing it decide how much that retiree is allowed to take away from those currently productive.
Finally, the millenia-old "retirement plan=loving children" means that how much each retiree gets depends on how many children they were able to have, how many of those survived, how productive they are, and how much they're willing to give up according to their character, how much they love their parents or how much social pressure towards supporting your parents there is.
