Be old dev doesn't mean that you know how to write code. I worked with devs with twenty years of experience, and I love it, and I learnt A LOT from them.

On the other hand, I worked with old devs too, and they did a lot of spaghetti code, they didn't make a module and a lot of things are weird for them. Like async/await/yield.

I think that it's not an old programmer, it's about the attitude that they had during his professional career and the attitude that they have now. With a lot of experience and the right attitude, I agree, it's a perk in the team!