I messed up in the above message when calculating the median:

  Clinton 46 years 154 days
  Obama 47 years 169 days
  Clinton second term
  Obama second term
  Carter 52 years 111 days
  Bush Jr 54 years 198 days
  Johnson 55 years 87 days
  Nixon 56 years 11 days
  Bush Jr 58 years 198 days
  Johnson second term
  Nixon second term
  Bush Sr 64 years 222 days
  Reagan 69 years 349 days
  Trump 70 years 220 days
  Reagan second term

The median is the age of Johnson, 1st term, 55 years 87 days