I may be wrong, but I think the problem is that startups are by and large unsuccessful across the board. It's a bit like trying to find the cause of a disease

I may be wrong, but I think the problem is that startups are by and large unsuccessful across the board. It's a bit like trying to find the cause of a disease by looking at what doesn't cause a disease. I did a quick search and got a lot of different answers, but the overwhelming number I got was that "over 90%" of startups fail in the first 3 years. With that, the number of possible common variables is going to be overwhelming. However, it does potentially answer the question of why successful founders tend to be in their 40's. If you have a 90% chance of failing in the first 3 years, if you start 10 startups, perhaps you have a good chance of succeeding ;-)