UA has hired some pilots in their early 50s, but pilots with significant experience. By doing so, the airline can avoid future age discrimination law suits.
Currently, U.S. Legislators are debating a Bill to raise the mandatory age 60 retirement rule for FAA air carrier, and Scheduled Commuter pilots.
Age 63 may be a compromise limit among those advocating no raise and those advocating a raise to age 65.
Curiously, ALPA is against raising the age limit. Airline managements are in favor.