I'm not a Gen Yer, but I must respond that the situation you describe really should be a teachable moment to the younger worker; explain to them why their idea may have been tried before and failed, or perhaps it was fundamentally unsound for a reason they hadn't thought of.
I agree that it should be a teaching exercise. But I've seen countless times where it turns into "Those old guys just don't understand!" even when they are explained, excruciatingly so, how their idea has already been attempted.
For example...I've had younger developers come to me with a brilliant new approach to development. Their idea? Basically, it was waterfall. No matter how much I explained to them that their idea had been tried and failed, they insisted that they were on to something new and exciting.
