Anecdotal: I'm a part-time CTO (long story) of a startup. I'm 30 myself. We hired 6 engineers in total up until now: three interns in their twenties, who're very smart and motivated but also inexperienced; two programmers with a few years of professional experience who can get to real decent (well written, unit tested, etc) code on the first go; and 1 guy of over 40.

When hiring, I was very skeptical of the guy over 40. His CV showed that he had spent most of his time building boring information systems for government agencies. This did not feel cool and startuppy at all. Also, he's gray-haired and he looks a bit dorky. We really liked him in person though, and he seemed to know what he was talking about, so we hired him anyway.

Only a few weeks later, I was already certain that he was the best hire we made up until now. Hypothetically, when forced, I would fire any two other team members to be able to keep him on the team (and he's on only half weeks). He's experienced, very much down to business, he cuts through the crap and through technical fads, and currently ensures that we're building the most lean and simple backend that I've ever seen. In a programming language that he's never seen before, and with a database engine that he's never used before.

For me, the general takeaway was that the wisdom to "not only hire copies of yourself" is very true indeed. More specifically, "older" guys (for tech industry standards) often have a lot more fundamental skills to bring to the table than perfect command of this year's technologie du jour.

Hire older people!