How is this a dark secret? This is true for almost all industries is it not? Most business want young hires because the work more (in quantity, not talking about quality here), and can be trained to fit the organization's needs.
No, in many industries experience is (or was) valued.
People businesses are generally worse though, look at law firms where the idea is to exploit the young, overwork them, and if they survive that offer them a tiny chance of the huge profits that senior partners share. Apparently this is supposed to be motivational.
