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Although, while more often than not true (perhaps partly due to survivor bias), I do think that it's not a given that old programmers are wonderful. Some older folks do seem very set in their ways and unwilling to experiment in a way newer programmers aren't.
The natural example is that you hear a lot of "ah it's like <blah> all over again" where blah is something like winforms or activeX or CORBA or lisp or OSGI or what have you, but it's frustrating to come into everything with that baggage.
Yes it might be the same idea, but it might be executed quite a bit better! Perhaps much wider platform support, perhaps lower total cost of ownership, perhaps increased viability under current conditions, perhaps much larger community of people and tools!
The cycle turns much quicker than it used to, and using older, more mature but inferior technology sometimes does have a big effect on the bottom line or provides a disadvantage over competitors in a way that I don't think it did as much earlier on. Granted, this isn't always the case and knowing when it is also matters.
I think "strong opinions loosely held" is a great motto, and a lot of these folks follow that motto to wonderful effect.
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It is also entirely possible do essentially the same project over and over in a multi-decade long career, and learn nothing material from it all, and I've seen that happen too.
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In conclusion, I think older programmers can be a great asset to your team, and are often overlooked for no good reason. But they're also people like everyone else.