"They're a growth incubator that pushes companies to grow fast over growing well."

Any evidence for this comment? Any evidence that there's even a tradeoff you can make? Any evidence that your hypothesis (which seems to be that "growing well" is better) is supported at all?

The reason (just guessing, not affiliated with YC) that YC feels like growing fast is best is that "growing well" might involve a greater investment before you've reached product-market fit.

I will also add that age-diversity has almost nothing to do with founders. Founders are already slightly older on average. Plenty of companies founded by young founders have their average age go up quite a bit once they have found product-market fit and can hire more people.

I am not familiar with Stross's book. If I remember correctly this subject is not part of the YC application (marital status, family...). I have applied three times including the latest for w2016. I have not been invited for an interview yet, so maybe it comes up in that context. For the record, I am single, no family, former aerospace engineer, laid off in my early to mid-fifties, several years ago. The topic of age diversity is of great interest to me. I believe there is a lot of engineering talent and experience laying dormant, waiting to be tapped - people laid off right before retirement. Adding to my defense systems engineering skills I've become a full stack developer for the project I am applying with, and I am ready to go!

(edited for typo)