He probably obfuscated that fact so people wouldn't judge him just by his age; it would seem based on some of the comments in this thread that he was right to do so.
Some of the best lessons in life can come from those who haven't been tainted by long stints doing the very thing they're commenting on.
Managing teams should be about the long term. Any understanding this guy has of the long-term
effects of his management style is necessarily second-hand.
It's not about age, but experience (and honestly representing yourself in the world).
N.B. I'm not saying he shouldn't write, or that he doesn't have valuable insights to offer, just that the author's experience is fair ground for discussion.
Some of the best lessons in life can come from those who haven't been tainted by long stints doing the very thing they're commenting on.