I can only answer from the Australian context.
In Australia there is no upper limit on the age to be an Air Traffic Controller. However, you must maintain four things to be an Air Traffic Controller:
- Air Traffic Control Licence: An Air Traffic Controller Licence will remain valid for the lifetime of the holder, provided the conditions specified in CASR Part 65 continue to be met, unless the licence is suspended or cancelled by CASA.
- Ratings: A Rating remains in force for the period for which the licence remains in force, or a period of 12 months, whichever is less.
- Endorsement: An Endorsementremains remains in force for the period for which the licence and the rating to which the endorsement is linked remains in force, or the period specified by the ATS Certificate holder (The ANSP) for a period no longer than six months, whichever is the less.
- Class 3 Aviation Medical: A Class 3 medical is valid for upto 24 months, CASA may issue a lower valid time if they want extra assessments on medical conditions.
Between these requirements most controllers retire in their late 50s to early 60s.
This is mostly due to degrading skills that mean that they don't pass there endorsement recertification checks or medical conditions either invalidate their medical or add restrictions on them.
But I have known one of the controllers hit 70, then retire without loosing any of the above.