Compulsory retirement in many countries is now illegal as it comes under age discrimination. For domestic operation in Australia it is my understanding that there is now no retirement age. But practically, if an airline operates internationally, it would have to retire its pilots at some point. This is because ICAO recommend, and some ICAO States (countries) set, a maximum age for pilots. Typically if the PIC is over 60 the F/O must be under 60, or vice versa. Then there is a cut-off of 65 for all commercial flying, period (USA, France etc).
The argument of skills declining with age has been done to death elsewhere in these forums. It is a very individual thing. I have checked pilots who were on the decline at 50, while others were still very near top of the game at 70.