I think there's another age-effect for new technology, that young people will learn that, rather than enhance their skills in an existing technology.

A test: if this is true, then fields with faster-moving technology (eg. silicon, software, internet, gene-sequencing) will have a higher proportion of young entrepreneur than in other fields (eg. earth-moving equipment, iron processing, civil engineering, fast-food). Of course, the faster fields will also have more entrepreneurs in absolute terms, because they'll have a greater number of disruptive opportunities, but here I'm just considering the proportion.

Statistically, there's also greater tolerance for risk in the young because no spouse, no kids, no mortgage.

Neither factor is intrinsic, and needn't apply to a particular entrepreneur.