I doubt many 40+ programmers are going to come out in support of this article. In cases of discrimination, you are labeled a crybaby so it's better to just stay quite. HN is mostly young and the only 40+ ones here are the type who like puzzles or in top 1 percentile of programming (e.g. patio11). For a vast majority of 40+ programmers, the reality is as grim as painted in this article.
If you are not in top 1 percentile of programming abilities, you better move to management. This is hard for someone who isn't verbally aggressive. Positions for management require X years of managing Y employees so if didn't make the move early on, you are doomed. Given that there isn't a puzzle/test type of way to rank managers, the management positions get doled out as opposed to competed for. You have to be in the shoes of a 40+ programmer who is not in top 1 percentile to know this :-(
Collecting data selectively is how discrimination starts.
But you are probably right, it's not illegal.