I think he has some valid points. The emergence of mobile and web 2.0 industries since the article supports rather than weakens his main argument.

just look at the evidence,

-founders of the most successful startups are always in their 20s or 30s. They don't have 20 years of programming experience.

-ruby, python, objective C are all fairly new

It means that a 50 year old programmer with 20 years of programming experience doesn't have too many advantages in learning these new languages / environments compared to a fresh college grad. In addition the 50 year old probably has a family and kids and other social obligations that reduces the amount of time he has to learn.

In other industries where the innovation isn't as fast, and the entire environment changes every 10 years, there is more value in seniority and experience.