Bezos did it, I believe.

Not necessarily their first startups, but: Dre (Beats), Larry Ellison, Travis Kalanick, Phil Knight (Nike), Jack Ma (Alibaba), Sam Walton, Wang Jianlin (Dalian Wanda). Mike Bloomberg and Amancio Ortega (Zara) were nearly 40.

I find it interesting which people you chose to label with their company and which you didn't.

I thought about that quite a bit as well while writing the comment.

Since HN is US- and tech-centric, I added the company name for non-tech or non-US companies. Walton was an exception because everyone knows Walton/Walmart, Bloomberg was an exception because the company's named after himself (and it is technically in technology), and Dre was an exception because (a) most people know him for his music, not Beats and (b) it's more of a fashion company than a technology company. I was on the fence with Ellison/Oracle, given how old the company is.

To save anyone else the lookup: Bezos was born in '64 and Amazon was founded in '94.