If the comments on the linked page are to be believed, it's worse than your assumption: Apparently Kauffman only selected "small businesses" with at least $1MM

If the comments on the linked page are to be believed, it's worse than your assumption: Apparently Kauffman only selected "small businesses" with at least $1MM annual sales and 50 employees. That excludes an awful lot of landscaping companies AND legitimate startups. My gut also says it skews a little towards older entrepreuners. Because it takes time grow to $1MM in sales, and I'd imagine that more young people found startups that fail than do 40 and 50 year olds.