Statistically, the shifts exist, but they’re not what the common assumptions are. Liberals don’t turn conservative; as I said, it’s more like everyone takes one step to the right, not two or three.
Part of what dims the progressivism of youth is just a little common sense. It sounds great to say “We need this and this and this program, and we’ll just tax the rich to pay for it”; but a little experience shows you that if you want all those things, you’re going to have to double or triple taxes on the middle class, which usually means on yourself. :-(
There are early indications that the next generation (whatever it may be called), that started in 1998-ish, being fed up with everything they’ve seen, may be leaning libertarian. Time will tell.