Should there be an upper age limit on the presidency? Former New York Mayor Michael Bloomberg, 77, may join a crowded and aging field of candidates. Last month Bernie Sanders, 78, was hospitalized with what the campaign called “chest discomfort” and turned out to be a heart attack. In September 2016, Hillary Clinton, then 68, was privately diagnosed with pneumonia. The campaign concealed the diagnosis until she was caught on camera fainting from dehydration.

Mental health is another concern. “Gaffes” on the campaign trail...