While that might be true (that young people are more easily manipulated) it doesn't make much sense as a primary reason for why VC's like young people.
Ultimately, making a big successful company is really hard and VC's would want to bet on people who have the best chance of doing that - not the ones they can easily screw with.
Note: I don't buy the idea that only young people make good entrepreneurs. There's tons of evidence that older entrepreneurs can be very successful. It's probably true though that young people in general are more likely to massively revolutionize something entrenched, even if their overall success rate is the same or lower than older people.
Ultimately, making a big successful company is really hard and VC's would want to bet on people who have the best chance of doing that - not the ones they can easily screw with.
Note: I don't buy the idea that only young people make good entrepreneurs. There's tons of evidence that older entrepreneurs can be very successful. It's probably true though that young people in general are more likely to massively revolutionize something entrenched, even if their overall success rate is the same or lower than older people.
Einstein, for example, was 26 when he published 4 papers that would change the field of physics forever: http://en.wikipedia.org/wiki/Annus_Mirabilis_papers