The proportion of credit-card debt in serious delinquency, meaning payments were late by 90 days or more, rose to 5.32% in the fourth quarter, the highest level in almost eight years, from 5.16% in the third quarter. The serious-delinquency rate for borrowers from 18 to 29 years old rose to 9.36%, the highest level since the fourth quarter of 2010, from 8.91%.
