There are two things to consider. Young people mind is still malleable and they are generaly free or duties and in a healthy condition. They can thus easily adapt, reconsider classic models and be totally commited to the startup with ne reasons to fear failure.

Older people tend to have a less malleable mind. They are slower to change direction and take decisions, but when they do, it is wiser and better thought than young people. They have to find compromise between the various external duties they have and can take less risk. They have less energy resources and endurance than young people.

From this perspective, it is clear that young people are more sexy for VC, because they are looking for innovative mercenaries ready to give their life and health for their company.

But not beeing sexy to a VC doesn't mean the project is rotten. The success depends on the project and the context. Beside there are many older people out there with a 20 year old innovative mercenary spirit and there are many young people out there with a 30 old guy's maturity.

So claiming there is a kind of use-by day for entrepreneurs doesn't indeed make sense.