Once you reach 60 years of age, under EU rules, you're not permitted to fly a commercial flight with passengers with someone in the other seat who's also 60 or over.
I suppose it guards against both pilots having a senior moment, or a stroke/heart attack, on the same flight.
You might argue that the risk is less than having two younger, relatively inexperienced, Oakley wearing, selfie taking guys, sporting enormous watches featuring many buttons which they never use .... but I suppose it's all about Threat and Error Management..?