What is the average retirement age of an architect?

It depends but Architects, just like any other creative professionals, doesn't really have an average retirement age. They work until they fall to death.

Take the Brazilian Architect Oscar Niemeyer. He died at 105 and his last actual project was an invitation in 2003, at the age 96, to design the Serpentine Gallery Summer Pavilion in Hyde Park, London.

Amazing.