New Delhi, April 11 -- Couples with big age gaps face unique financial challenges. When children are still at home, those challenges multiply, forcing families to balance retirement, college funding and financial security.

Most U.S. couples are close in age-about two years apart on average. But census data show that roughly 8% to 9% have age gaps of a decade or more, putting partners on staggered financial timelines.

"We've got college staring us down in 10 years," said Annie Galvin, 44, a marketing professional in Washington, D.C., whose husband is 54 and whose son is 8. "My husband will be eligible to retire right around the time our son starts college."

Galvin said they have built retirement savings, a 529 education-savings plan and...