Couples with age gaps face financial challenges. How to navigate them.

. in New York. The typical 20- to 30-year retirement can stretch to 35 years or more with an age gap.Even when families recognize that extended timeline, advisors say they often underestimate how costs evolve.“They don’t tend to think about the full cost of bringing up and educating children,” or the time it can take to fully launch them, said Dan Beckerman of Beckerman Institutional in Ocean Grove, N.J.That disconnect can have consequences.

In one case, an American investment banker in London who had earned a high income for decades—and never felt pressure to plan—continued paying a daughter’s housing costs into her 30s. When he retired, repatriated, and later faced health issues, that approach became unsustainable, leaving less money for a child from his second marriage who is still in high school.One of the biggest risks comes when one spouse retires or reduces income while expenses remain high with children at home.

Oestreicher of Spinnaker Trust said it is important for the younger spouse to continue saving during these years, even as the household begins to draw down assets.Required minimum distributions (RMDs) from retirement accounts can complicate cash flow, sometimes forcing withdrawals sooner or in larger amounts than planned.The good news: When one spouse retires, the couple may end up in a lower tax bracket. That can be an opportunity to convert tax-deferred retirement accounts to Roth accounts, since the converted amounts are taxed as ordinary income.Oestreicher said it often makes sense for the older spouse to delay Social Security benefits and the younger spouse to claim earlier.Delaying the older spouse’s benefit increases the eventual survivor benefit, while earlier income from the younger spouse can