It's the same if you sum it up across the population: all the benefits that elderly consume without producing are subtracted from what young people produce without consuming.

If you want your parents to retire earlier than the population-averaged system can allow, you're free to do it a non-averaged way.

Then, as a matter of fact, he'll have to rely on someone else's kids to feed him, whether directly or through taxes.

If he voluntarily chose not to raise kids, not even adopted ones, then he placed himself at the mercy of strangers. This may or may not end well, depending on how much spare resources they have.