Of course, age discrimination is illegal, wrong, and shortsighted. The PR profession will probably never have this problem, as hard-earned experience tends to rule the day at the most senior levels. But it does make you wonder what prejudices lurk beneath the surface.
One perception that I know exists is that non-agency people are too difficult to integrate into a firm. Thus are many potentially great people passed over. In fact I know several people who have come up through a non-traditional route and would love to join an agency. But they are constantly rebuffed, in the nicest, most circuitous way (after all, they may be clients one day, right?).
The PR industry needs MORE people - do we get that? It's growing, but its perceptions of what people can do, and how a firm can adapt to help them, is not growing at all.