California Code, Business and Professions Code - BPC § 3523

All physician assistant licenses shall expire at 12 midnight of the last day of the birth month of the licensee during the second year of a two-year term if not renewed.

The board shall establish by regulation procedures for the administration of a birthdate renewal program, including, but not limited to, the establishment of a system of staggered license expiration dates and a pro rata formula for the payment of renewal fees by physician assistants affected by the implementation of the program.

To renew an unexpired license, the licensee shall, on or before the date of expiration of the license, apply for renewal on a form provided by the board, accompanied by the prescribed renewal fee.