Founders of health and biotech unicorns are older on average, Ali Tamaseb said. The notion of the teenage and twenty-something technology entrepreneur looms large. In reality, the most successful companies are more commonly founded by people in their 30s or older. Among startups valued at $1 billion or more created over the last 15 years, the median age of the founders when starting their businesses was 34, according to research in a new book called Super Founders: What Data Reveals About Billion-Dollar Startups. The finding offers new evidence that leaders with some experience bring advantages, said Ali Tamaseb, the author and a partner at the venture capital firm DCVC. "There are, indeed, many successful billion-dollar startup founders in their early twenties," Tamaseb wrote in the book, "but most of them aren't." His takeaway: Age doesn't matter.