From your first link, this is the key passage.
People are conflating two data points (startup founder and average age of a business owner when they founded their company). The later is a bigger population than the former.
"Startup Founder" is synonymous with growing a business to be huge, so you should exclude founders from the calculation who are NOT attempting to grow a business to be huge.
I imagine when you exclude said individuals, the average age of a "startup" founder to be much younger.
https://hbr.org/2018/07/research-the-average-age-of-a-succes...