Why good people leave large tech companies

Observation: So if it had been the practice to hire "adult supervision" for young innovative founders at startups, why is there such a disparity in the number of startups with individuals with great ideas, Drive and ability who are in their 40 to say mid fifties. Given that most startups are rapidly grown and acquired or go public in the first 5-7 years, if that long, surely SV can see the benefit of funding startups based on idea, Drive and ability rather than just on age, idea, etc.

Out of curiosity, what are the ages of the oldest startup team ever to go through Y Combinator? Not the average age of founders but the oldest. The application clearly asks for founders ages but is there a cutoff age that would not even be considered regardless of idea?

  Over the six months after his department relocated to the East Bay, 55 of the 70 employees in his group
   who were asked to relocate left. 25 of them joined his new startup.

This sounds to me like sabotage on his part, planning to harvest preferred members of that team for is own interests.