I don't think that's really testing the argument he's making. He's arguing that people are more likely to start giant companies on their first go round, not that they're more likely to prefer cofounders who're on their first go round.
When you're looking for a cofounder, you're naturally biased toward someone with relevant experience, because the whole point of recruiting them is so that they can add value to the business and increase its chance of success. But when you're the initiator, a large portion of your contribution is picking the initial direction of the company, and what it's trying to accomplish. It's quite possible for first-time entrepreneurs to pick more ambitious goals and yet have less of a chance of success than repeat entrepreneurs.
When you're looking for a cofounder, you're naturally biased toward someone with relevant experience, because the whole point of recruiting them is so that they can add value to the business and increase its chance of success. But when you're the initiator, a large portion of your contribution is picking the initial direction of the company, and what it's trying to accomplish. It's quite possible for first-time entrepreneurs to pick more ambitious goals and yet have less of a chance of success than repeat entrepreneurs.