Even if men and women retire at the same age (in many countries still not the norm), women get to use this system more - society gives them 45% more.

How many? It's an average of 5 years globally. Given a retirement age of 65 and an average life expectancy of ♂️76 and ♀️81, that means that a woman is getting 45% more of this system.

Of course let's not forget, that men have had a heavier toll on their body while working (even if something not as taxing as construction or police work) because of more night shifts, exposure to chemicals etc, therefore these last years are bound to be less enjoyable.

Check your country on Our World in Data

Explanation: In countries with a retirement age, the system is not rewarding personal investments, but it is creating a taxation on current working population, so that older members of the community have a decent standard of living.

This system is based on life expectancy vs workers contributions (%wise on salary and numberwise). Yes, pensioners have contributed throughout their working lives, nonetheless, this money was used to pay the pensions of the previous pensioners. Current working population is financing the end of life of current pensioners through their pensions (and through the universal healthcare system - where available).

PS: This is not an argument against state funded pensions: There is of course political reasoning behind this: older people are freeing up working positions and the expectation of a society taking care of its elderly creates trust, that empowers people to be more daring in their ventures. Children are also freed from the financial burden of having to take care of their own elderly.

PS2: The math is a little bit more complicated, as the deaths are not equally distributed throughout the whole life expectancy curve, but you get the idea.