MariaDB from 2009, based on MySQL from 1995.
PostgreSQL from 1996, based on Postgres95 from 1995, based on POSTGRES from 1989, based on INGRES from 1974(?).
I wonder if any lines of 1970's or at least 1980's code still survive in some corner of the PostgeSQL code base or if everything has been rewritten at least once by now? Must have started out in K&R C, if it was even C?