As you get older, there's a lower chance you'll fail due to internal reasons, but a lower chance you'll start (eg. less risk-seeking, less geographically mobile, family commitments, debt, etc.).
By this logic then, I'd expect VCs would jump at the opportunity to work with older, more experienced entrepreneurs who happen to be free from those commitments.
I would say the younger you are, the better your ability to acquire entrepreneurial spirit, but the less knowledge you have to execute. The older you are, the more knowledgeable you are at executing yet the more shy you become at dreaming big.
This makes me recall the phrase: An entrepreneur needs the right balance of genius and craziness.