(a) Notwithstanding any other provision of law, the death penalty shall not be imposed upon any person who is under the age of 18 at the time of the commission of the crime. The burden of proof as to the age of such person shall be upon the defendant.
(b) The penalty for a defendant found guilty of murder in the first degree, in any case in which one or more special circumstances enumerated in Section 190.2 or 190.25 has been found to be true under Section 190.4, who was 16 years of age or older and under the age of 18 years at the time of the commission of the crime, shall be confinement in the state prison for life without the possibility of parole or, at the discretion of the court, 25 years to life.
(c) The trier of fact shall determine the existence of any special circumstance pursuant to the procedure set forth in Section 190.4.