I think this begins to be visible even sooner, 38 if you graduated at 23. The majority of the job market requires very very few 15+ years experienced engineers. 5 to 10 years of experience is a sweet spot - you will be easily hired. Everything below and beyond is a struggle, especially for the latter since very few companies need and are willing to pay for those skills.

And that's how you become unemployable with the irony of being at more or less what would be the peak of your technical capabilities. In years later on, people start to lose the drive.