There was an argument on twitter over some advice a recruiter gave: don’t hire anybody over the age of 30.
This was not popular advice. He clarified later that he wasn’t specifically telling people to discriminate based on age, but that there is no alpha in people who have enough datapoints on their resume because they are too easy to assess.
And nobody liked that, either.
Which is a shame, because he is telling the truth.
There are twin studies that model the causes of income — within men, the correlation between MZ twins in income is about .45, which rises to .51 when using 5 years of income data, and then to .63 when using 20 years.

The correlations vary by country and sample, but the logic checks out: the factors that cause variance in income between years are less genetic than the ones that cause differences between people.
A correlation of .63 between MZ twins reared together implies that environmental factors not shared by siblings explain 37% of variance in income, though this is not necessarily luck — traits that cause income like personality and intelligence are not perfectly heritable. Even if income was not determined by luck at all (which is almost certainly not true), this observation would not be unexpected.
The underlying argument here? Life is largely fair. If you fail once, that might be bad luck, but if you fail multiple times, then you’re just a loser.
Ignoring the hereditarian defense, the incentives to become high status are stronger in the young than in the old for three reasons. Part of the reason is that status is age-relative: a 20 year old with a net worth of 5 million is more impressive than a 70 year old with a net worth of 50 million, so the youth have more to win by playing the same status games. Status also translates more easily into success with the opposite sex at a younger age, as most people pair off into permanent relationships in their 20s and early 30s.
II.
Rabois’ advice of not hiring people past a certain age was illegal, but that was not the reason why people were so mad at him. It was because people do not like systems that discriminate based on features that cannot be manipulated by incentives — it’s more socially acceptable to exclude criminals or people without credentials than the unintelligent.
There’s game theory behind it. Imagine an island where selecting employees based on criteria that cannot be changed by incentives is banned, which are intelligence, personality, genes, family background, facial structure, and demographics. The idea is that if status is determined by more malleable behaviors, then that will be a net gain for everybody as people will try harder to change the things that they can change. If an employer were to ignore this and select employees based on characteristics that are immutable, then they would have better employees, but they would make them the defectors in the national game of hiring.
Ageism is also deterministic, which has negative connotations. The idea that somebody who has achieved nothing at the age of 38 is never going to make it is constraining, unempathetic, and gauche. But it’s true. (Well, technically it is not, but it’s true for the vast majority of people in that scenario).
Anti-ageism, at its core, is the same as any other manifestation of slave morality.
Oh yeah, and we are back to Sebastian Jensen. Names stick, and the fake name is better than the real one.
Imagine you have to hire a childcare worker. You can’t interview candidates and all you know is the candidate’s sex. You have one male and one female applicant. You will inevitably pick the female.
Repeat the game where all you know is age. You have an entry-level position in an IT firm and one application from a 25 year old and another from a 55 year old. You will inevitably pick the 25 year old.
In the real world there are lots of other factors about the candidates that might make you hire the male for the childcare position and the 55-year-old for the entry-level position in the IT firm. But these candidates will have to help you to overcome your logical suspicions about their ability based on their demographic characteristics.
I made a big career move just after the age of 40 several years ago for a few reasons. One of the major reasons was that very soon I was going to be too old to be considered a credible candidate as an external hire no matter what my experience was.
Is there a common form of discrimination that is never or rarely rational? Probably not. That's why there are laws and rules against it.