In practice (I have experience with union labour), it depends. The older workers will usually step forward in negotiations and secure plum benefits for themselves, very often at the expense of younger workers.

Don't get me wrong - I think everyone does better with union negotiations (even managers to some extent - at least with a union contract, everyone's expectations are clear). But it definitely pays to be represented there at the negotiating table. It's a challenge to convince the younger workers to take an interest in this.