Ask any eye doctor and they will tell you people start to lose their vision in their late 30s and need reading glasses by 40. It is true in technology too. Dave Winer disagrees with Fred Wilson on this. Technology visionaries lose their "vision", but not their brains, by the time they hit 40.
There are rare exceptions. Steve Jobs comes to mind. But if you look at the most innovative startups today, or even 20 years ago, they were mostly started by people in their 20s. Facebook, MySpace, YouTube, Google, and lots of others were started by "20-somethings". Back in the Web 1.0 era, Netscape, Napster, Paypal, Amazon, and many others were again, started by "20-somethings". And way back when...Apple, Microsoft, Sun, Lotus, and many others were started by "20-somethings". It is hard to remember a significant "new vision"startup that was started by someone in their 40s.
Young people have vision for what is possible, and are not blinded by "knowledge" of what is not possible. Young people are great at starting things, but in most cases, not so good at building big businesses. There are of course exceptions here too. Steve Jobs, Bill Gates, Scott McNealy, Mitch Kapoor, and a few others were great visionaries AND good at building large sustainable businesses.
Older, more experienced people ( I am an old guy) are typically better at taking a startup idea and building it into a business. Older people are great at understanding the potential of "paradigm shifts", but not great at seeing them beforehand. Just as our eyesight fails us in our late 30s and 40s, our vision, or ability to see and predict the future also fades. Once a young visionary brings the idea into focus, us older guys quickly understand the implications and how to capitalize on it.
Don't get upset about it. It is just the natural order of things. Yes there are exceptions. Fred Wilson, and most VCs, are just watching the trends...and they are pretty clear. Investors are looking for companies with young technical visionaries supported by older business and marketing guys. That is a winning combination.