I spent 18-22 enrolled at one university earning a degree in the major that I listed on my application packet, but I interned at a different company each summer. If I'd worked during the academic year, I'd probably have had several additional jobs during the period: folding towels at the gym, computer laboratory attendant, resident advisor, off-campus food service and off-campus retail.
Similarly, one could argue that people accumulate debt 18-22 because their immature brains are too stupid to understand cause and effect, ignoring more salient facts like: 1) 18 year olds have not had time to establish specialized professional experience so their earning potential is low due to no fault of their own 2) Immigration and trade policies have deliberately and drastically reduced the earning potential of unskilled labor (which includes basically all 18 year olds, including future MD's and PhD's) 3) Housing costs and especially education costs have skyrocketed in the past 40 years 4) Education is increasingly financed through debt rather than loans.
This is not as much fun as "kids today are so stupid!", but IMO a far more accurate explanation for why a current college student will incur more debt than a Boomer who could earn enough each summer hauling hay or working in a unionized factory to pay a year's tuition at State U.