The truth is that a VC sits on a portfolio of undervalued options. A success among pool of startups is always a non-linear event. It is a meteoric rise, a market-share grab which often actually creates a completely new market. A very few successful startups will make a large pool of dog investments still a very profitable business. One option will fire, the rest will expire worthless.
That's why a VC has to drive all of his startups towards increasing risk and trying to grow big, fast. Go for a large team. Invest, borrow, rise capital. One of you will win, the rist... what do I care?
Now, from the point of view of entrepreneurs, they often get a very poor deal. An engineer has only one option in his portfolio -- that is his venture. Its success is largely dependent on random factors like stumbling on a network effect, or tapping a new undiscovered need of millions. What would be a true price of such an option?
Whatever the price, young guys have poor bargaining power at the negotiating table facing seasoned VCs. Older guys do better. For a young guy a startup is not only a way to riches -- it is also a way to self-actualise, to define one's identify. An old guy does not need this crap. He has accomplishment behind his belt. He can drive a hard bargain and to get better deal from a VC. He is driven to get a good business deal, and will not go dancing across the room just because his name features in some crappy termsheet.
An old hand is also more likely to take less risk and to shoot for a long term, VC appetite be damned. They will be practicing more 37signals-like approach. Profitable? Have positive cashflow? Great! And fuck your IPO plans, at least until I feel the time is right.
So, it is no wonder that older founders have better success rates. They exploit the VC industry when they want to, not the other way around.