old guys
wikipedia says:

The oldest president to assume office was Ronald Reagan (age 69 years, 349 days).

so he was not quite 78 when he left office.

ron paul turned 76 last august. he will turn 77 before the next election and 78 during the first year of the subsequent presidential term. if elected, he will set presidential age records every year he serves.

say, why don't we repeal the 22nd amendment so he can be not only our first octogenarian president but our first nonagenarian president too? i mean, if he lives....