Somewhat grim, but this has to be disregarding the humans who never reach the reproductive age or the ones who cannot keep their offspring alive. So there is some survivorship bias baked into the methodology.
'Is this study disregarding the humans who never reach the reproductive age or the ones who cannot keep their offspring alive? Is there is some survivorship bias baked into the methodology?'
You might find out - we might find out - rather than you guess wrong, never find out, and we all carry the error with us.
Problem is, the internet is also filled with studies that prove or disprove anything you want, best to be skeptical.
I personally don't put much credence into any studies that seriously thinks they can make any factual accurate statements about things that may or may not have happened 250,000 years ago. Science is never settled.
From the comments, it is pretty clear to me that people lack understanding of biology/modern computational genomics, and the models used and their limitations.
"Average age of people who gave birth include people who never give birth?" or "Is a selection bias to include only people who gave birth in the selection of people who gave birth" sound completely different if asked this way, right?
So everyone who has a parent is included - which is everyone who ever lived.
From a non-expert reading of the article, their pipeline is more like: modern human population genomes -> estimates of modern mutations' ages -> estimate of average historical parental ages.
The first estimation (genome -> mutation ages) was carried out in a prior study "GEVA" [1], and this paper's contribution seems to be estimating the average parental ages based on those previously estimated historical mutation rates.
I couldn't find any mention of using old DNA samples. The GEVA study pulls from two genome databases, TGP [2] and SGDP [3], both of which seem to be entirely modern genomes. I'm not an expert in the field, so maybe it's obvious to a population geneticist that these databases do include old genomes.
Given that they're only using modern (surviving) genomes, the critique of survivorship bias seems valid.
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6992231/