I tried to do SQL Subtract exactly a year but the syntax in PSQL didn't work. In my case dates were imported with 2 digit years so they all have birthdays off by 1900 years.
UPDATE patients SET birthday = dateadd(year, 100, getdate(birthday)
throws:
ERROR: syntax error at or near "table"
LINE 1: UPDATE table SET datefield = DATE_ADD(datefield, INTERVAL 1 ...