A corollary: software engineering interviews are tests. When you are young you can memorize more things. When you are older you've experienced many different ways of building software. But, interviews, most of them, generally just ask you to regurgitate concise facts, just like PG points out tests do. And, our brains are tuned to pick out mistakes in those facts and make decisions based on that. I'm not saying hiring for engineers is biased against older engineers, but it makes me think after reading this essay.