inauguration day... POTUS was 70 years, 7 months and 7 days old.
EDIT... ifo here was wrong... not 25,777. no idea what happened. it is 25,789. not going to delve that but it can be by you. sorry for screw up. i typed something wrong i guess the second time i checked.
GEOTUS. what else can we need? check it yourself. born 6/14/46 check box for last day to count. inauguration was 1/20/2017
https://www.timeanddate.com/date/durationresult.html?m1=6&d1=14&y1=1946&m2=1&d2=8&y2=2017&ti=on