TheBoost said:
I imagine that being a Jedi is a calling, not a job you retire from.
Apparently you’re right. According to the Dooku article on Wookieepedia,
Dooku's abrupt departure surprised and disturbed the Jedi Order. As a Jedi Master who had voluntarily resigned his commission, Dooku became part of the group later known as the Lost Twenty. In over two thousand years, only nineteen other Jedi Masters had walked away from the Order.