Many just loaf around with parents money.
That is why most people dont grow up till 25 now
I don't think this is at all accurate, even as a generalization.
Going to school full-time, first in HS, then in Uni is not 'loafing'; or if it is, you're doing it wrong.
I don't think having a job during HS is at all essential; if one can do so expressly in summer for a few weeks, or if we're talking about the odd lawn mowing or snow shoveling for a neighbour, sure...
But I'd rather students focused their energy not only on graduating but doing doing with good marks, rather than making pocket money.
Once at the Uni age, its certainly wise to get a summer job, especially when you're off for the better part of 4 months. The experience is useful.
But I don't think the stats support a huge decline in summer employment by those over 19; it mostly shows a substantial drop in teenage employment, which I see as a positive.
Lets add that some of the drop in teen employment is actually a drop in full-time employment of dropouts, who now graduate HS.