What age do you think parents should stop "disciplining" thier kids at?

When they are no longer under their care

when they get a job and move out!

20, when they cease to be a teenager. Then it's up to the new adult to take what has been instilled in him/her and forge their way. Parents will always give advice, whether you like it or not, but their duty to discipline ends with adulthood.

If you mean when should they stop punishing your wrong doings when they are no longer responsible for you.

Why have you put "disciplining" in quotation marks?

as long as they need it they should get it no matter what age.