Where did you get that from? The article mentions changes at age 9, 32, 66, and 83.

It's just the popular wisdom these days. Companies tend to deprioritize hiring engineers in their 40s, especially if their overspecialized. At face value, Companies want high-energy 20-somethings that they can mold into their specialty. More likely, they know that 20-somethings expect a far smaller salary.