Today, Americans are collectively struggling with a trillion dollars in student loan debt. That's hitting borrowers of all ages, of course. But which age group has the hardest time keeping up with the payments?

That would be people aged 40 to 49 -- nearly 12 percent of which have fallen more than 90 days behind on their student loan payments, making them the only age bracket with default rates in the double digits, according to the Federal Reserve Bank of New York. By comparison, the delinquency rate for twenty-somethings is only 6.2 percent, possibly because borrowers in their twenties often have the option of deferring their payments, according to the Los Angeles Times.

Still, with unemployment so high, keeping up with student loan payments has proven difficult for all age groups. The student loan delinquency rate hit its highest point in over a decade last year. In addition, as of March, student debt increased by 148 percent overall since the beginning of 2005, according to the New York Fed.

It doesn't get much better after your forties either. Nearly 16 percent of Americans over 50 are still paying off their education, according to Barclays. In addition, the share of retirees still paying off student debt increased by 62 percent between 2007 and 2009.