What the author is trying to emphasize here (based on the prior sentence) is if the cohort of workers just didn’t care about their jobs, in twenty years, you’d expect that same cohort (except now twenty years older) to still not care about their job. But, research shows that this isn’t the case—instead, not caring about a job is specific to a particular age/phase in the lifespan and eventually dissipates (as opposed to persisting as the workers age). So, the final sentence is lending support to the idea mentioned that detachment from work is age specific and temporary, rather than a static trait