Debt among Americans in their 60s has surged since 1998, largely because more of them have mortgages and are paying them off more slowly. Research presented by the Urban Institute at the August Meeting of the Retirement Research Consortium highlighted these and other aspects of debt among older Americans.

The blog by the Center for Retirement Research at Boston College reported that nearly two-thirds of Americans in their 60s carried debt in 2010, up from just less than half of that group in 1998. In those 12 years, debt increased from 10% to 18% of the assets held by this age group.

More debt in this age group doesn’t directly translate to higher retiree debt, because many baby boomers are waiting longer to retire, according to the Bureau of Labor Statistics.

However, greater debt may be behind the decision to put off retirement, Urban Institute research indicated. A separate study presented at the consortium showed that 17% of mortgage borrowers nearing retirement age are underwater on their home loans.

The number of indebted Americans in their 60s rose among all income levels: 70% of the top third of earners held debt in 2010, an increase from 57% in 1998. The share among the middle third saw an increase of 17 percentage points and the low-income third saw a 14-percentage-point increase in debt holders. The consumers in each income bracket owed more than their 1998 counterparts.

More from Credit.com

• The First Thing You Must Do Before Paying Off Debt

• 3 People Who Dug Out of Deep Debt

• 5 Ways to Get Out of Debt: Which Will Work for You?