Very well said. From my experience as a check airman and dealing with Professional Standards cases I would say these guys complaining about flying with "old guys" are themselve probably the weak link in the cockpit.
I've seen sharp pilots from all age and background demographics. Any breakdown in cockpit professionalism is almost always a result of both Captain AND F/O being at fault. It's a team and it takes two to let weak behavior become a problem. If one guy is making a mistake, the other can either rise to the occasion and not let the minor problem become a big one or he can be a butthead and make the situation worse than it has to be.
One thing for sure, if a guy is having multiple problems with fellow crewmembers, he needs to look in the mirror to find the source of his problems, not at someones birth certificate.