So when you find someone good at code, you want to make sure to move them out of coding when possible and into something that skill and understanding of programming has no bearing on: management. [edit: removed pointlessly antagonistic remark]
2. Without opportunity for advancement, your best young talent will apply to YC.
3. Having managers which understand the technical aspects of the projects they manage, doesn't hurt.
1. In the US...
But AFAIK, hiring the older worker on the basis of age would never be illegal. Discriminating against an older candidate is illegal in certain circumstances, but not always.
http://www.eeoc.gov/facts/age.html
In practice, such discrimination appears to be commonplace and virtually unpunished given the burden on the candidate to prove that discrimination actually occurred.
Considering that there were 22,000 Federal age discrimination claims in 2009 [http://www.eeoc.gov/eeoc/statistics/enforcement/charges.cfm] and that 61% of all claims were considered to have no reasonable cause and 17% were closed administratively [http://www.eeoc.gov/eeoc/statistics/enforcement/all.cfm] one could napkin estimate that about 5000 people had some success in claiming age discrimination. I'd be willing to bet that most of those successes were against an employer and not related to the hiring process.
Not that any of that makes it right.
So if I'm looking at succession, I'm probably going young. If I'm looking for someone with enough sense to avoid re-inventing the wheel, I'm probably going mature.
[all of which is somewhat irrelevant to the effects of unemployment].