I'd expected that to be true, but as far as I can tell, it seems like there's a large segment of adults in their 40s/50s who have tens of thousands in debt and

I'd expected that to be true, but as far as I can tell, it seems like there's a large segment of adults in their 40s/50s who have tens of thousands in debt and are unlikely to pay it off: https://www.axios.com/2023/06/30/student-debt-age-gender https://www.axios.com/2023/06/30/student-debt-age-gender . This, combined with the younger demographics containing people on their way to repaying quickly or still accumulating, means that average is actually higher for older borrowers (even while the probability of being a borrower goes down with age).