A total of 16% over-50s still have the burden of a mortgage, but this figure rises to 26% for people going through a second marriage or long-term relationship.
People who have had children with a second partner, known as second lifers, have an average mortgage debt of £73,881 to pay off compared to £62,836 for over-50s generally.
As many as 22% only expect to clear their mortgage when they are between 66 and 70 years old.
Andrew Strong, chief executive of Saga Personal Finance, said: “The later-life parenting trend suggests that debt may remain a problem for many people as they get older.
“The endowment mortgage crisis and age discrimination in mortgage lending is impacting on some over-50s at a time when they may not be able to generate additional income to cover the cost of a mortgage or other debts.
“A tax-free lump sum provided by equity release could help relieve some of the pressure.”
More people are having children later in life, as 22% of over-50s had their last child between 29 and 31 years old, while the number of mothers aged over 40 has more than quadrupled over the last three decades from 6,519 in 1982 to 29,994 in 2012.
Having children means many are burdened by added non-mortgage debt, such as university fees.
Of second lifers 16% have non-mortgage debt, accounting to £13,652 to pay off, compared to £10,830 for the rest of the over-50s.