Compulsory with Eurocontrol at 55. However ezxcptions are possible, in the Ops Room if there's a controller shortage but more usually in the Sim. (I was surprised at some of the names that turned up there. Maybe a case of who, not what, you know.)
I walked free medically at 53 and was invited to come back "just as a Supervisor, not a Controller", a request I was very happy to turn down.
By 55, you're starting to slow down, mentally and physically. Canteen meals rot your guts and trying to get any rest on a night duty is impossible unless your employer has built a five star hotel next to the Ops. Room.