Young people are very popular because they don't know how to negotiate their worth and hence are cheap. Older people may be more experienced but compared to hiring two or even three (more?) younger ones they will produce less code that will (probably) be less buggy and a bit better laid out but you won't be able to get them to sleep under their desks or work unpaid overtime. And those other advantages won't show right away. So in the end the younger guys get more done for the money and they are probably a lot more pliable.
That doesn't seem consistent with your first post. Overall, would you argue that older engineers do or don't suffer worse outcomes because they require higher pay? Is it the case that employers hire younger engineers instead, or is it the case that in the long run, older engineers get jobs at the higher pay they demand?
Younger people tend to be the ones hired early on in the life cycle of a product or company because they're cheap, easy to push into a mold (or so management likes to think) and can do just as good a job (or maybe even quicker) than older people in making something that visually looks like it might work.
Then, as the project matures you'll find that that gained speed comes at a price, a price that will sooner or later offset the higher wages demanded by the ones that are further along in their life (dependents, more aware of their value).
If there are young really good programmers (it does happen, I've met a couple) then they tend to be exploited even worse, they will end up creating a large amount of value for peanuts.
But that's rare enough that it doesn't change the situation too much.
So I don't see any inconsistency, it's just time shifted.
