Donald J. Trump and Hillary Clinton have been more secretive and selective than many recent presidential nominees in providing up-to-date details about their personal health — a particularly striking departure, experts say, given the candidates’ age.

No American election has ever featured two major-party nominees as old as Mr. Trump, 70, and Mrs. Clinton, 68, and they have kept a grueling pace for more than a year. Yet they have declined to share the latest information about their health or to make their doctors available for interviews. Each released a brief medical statement in 2015; neither has added to it since.

Mr. Trump has been especially unforthcoming, even as he has sought to turn health into an issue in the presidential race, questioning Mrs. Clinton’s “physical and mental strength and stamina” as his allies push unfounded rumors that she is ill.

Hope Hicks, a spokeswoman for Mr. Trump, said Monday that he would have “no problem releasing additional records” about his health if Mrs. Clinton did the same. Advisers to Mrs. Clinton, who has released more details than Mr. Trump, said the onus was on him to match her disclosures.