I think this site and the referenced bloggers have a software-centric focus. There may well be a significant number of successful 20-somethings in software businesses. But software is a subset of technology and one cannot apply the observations here to technology in general.
Consider this: the global market for communications equipment exceeds 1 trillion dollars -- there's a lot of opportunity there for domain specific expertise that often times requires an advanced degree and experience in the industry. Companies such as Qualcomm and Broadcom are other examples where the founders were well-established in their careers, i.e. not 20-something.