Or perhaps their parents are better off, more people are going to college, so fewer of them are forced to work menial jobs to pay the bills. I have no idea if that's true, but that's kind of the point; you have to dig deeper.
https://www.epi.org/publication/charting-wage-stagnation/
suggests that, in inflation adjusted terms, most workers wages are up a modest amount (6%) since 1979, while the 10th percentile workers have declined by 5% in that period.
The employment to population ratio has fallen 5-6% over the same time period (and 10% from its peak) . It may be recovering somewhat now, but it's not part of the charts and not close to the peak.
https://en.wikipedia.org/wiki/Employment-to-population_ratio
Worse still, comparing to household income, you see that a higher employment ratio is necessary just to maintain the income. That causes childcare, prepared food, and transportation expenses to rise faster than inflation... because even if prices are constant, more people need them. That's ignoring the falling percentage of jobs with insurance and pensions that that also reduce total compensation... it also ignores stock options.
It was common for 12-18yr olds to work part time at groceries, fast food, retail, theaters, delivery to earn gas money or save for a car or college/trade. That is largely gone. Those jobs seem to have been taken by desperate adults and seniors.