The article is not good, sorry.

For instance, it begins via:

"How heritable is hair color? Well, if you’re a redhead and you have an identical twin, they will definitely also be a redhead."

So, red hair is primarily caused, in most cases, by a defective enzyme involved in pigmentation. Wikipedia mentions it: https://en.wikipedia.org/wiki/Red_hair - you can read up on pubmed for that https://pubmed.ncbi.nlm.nih.gov/10326071/ and more recent articles. Now why is the claim "identical twins" must be redhaired? First it assumes that identical twins are fully identical on the genetic level. This is not the case, there are many differences. Statistically these are, of course, much less than when you compare many different people to one another usually. So it can be assumed that in most cases the "identical" twins (a better term would be monozygotic; note that even wikipedia here https://en.wikipedia.org/wiki/Twin defines the word incorrectly. Monozygotic does not say ANYTHING about "identical". Mono means one; zygotic means "from the zygote" or "derived from the zygote"). Of course in most cases the genes, if compared 1:1, will be identical. But this is not always the case, and it also depends a lot on the mutation at hand (or rescue mutations - see genetic cosuppression). So it COULD be that identical twins are NOT both redheads. One possibility is a simple spontaneous mutation at a nucleotide position that could restore functionality of at the least one enzyme mentioning above with regard to pigmentation. During DNA replication errors can also happen. The rate of error creation may be low for many reasons, but it is above zero, so it could happen.

That problem in the article could have been avoided if he would have chosen something else other than "they will definitely also be a redhead". Other users here on Hackernews also pointed out other incorrect or incomplete statements or assumptions made. This also ties into "definitions". Ultimately there is a much easier definition first: define max age span and average age span of cohorts. Then you need to define heritability with this regard. The claim of "more or less life span" when heritability is redefined, means that someone did a very poor, sloppy job beforehand already.