"Presidential candidates" is a tricky term to define, and a large dataset to gather. Taking the ages of Presidents when first sworn in (comparitively easy data to obtain), and assuming that this is a good approximation for age of candidates despite the notes below, it looks instead like the median age has, broadly, been decreasing.
- Grover Cleveland has only been included once, despite serving two non-consecutive terms.
- Age on swearing in is not the same as their age on election day and, as the date of inauguration day changed following the ratification of the 20th Amendment, the difference between Election Day and inauguration is not constant across time.
- Some of the Presidents included here took over as the result of death or resignation of their predecessor, so weren't elected as President prior to their swearing in.