I need to install older version of mysql server on mac os, but I have a newer version.
I tried to remove this newer installation (5.1), but when start old version instal
I believe you can essentially just delete the /usr/local/mysql-Version/ and unlink the /usr/local/mysql directory. Getting rid of the system pref and the start up item might be harder, but I didn't install those so I can't help there.
/usr/local/mysql-Version/
/usr/local/mysql