What is the test for a minor to make a voluntary statement to the police?

In People v. Lara, 67 Cal.2d 365, 62 Cal.Rptr. 586, 432 P.2d 202, it was held that the capacity of a minor to make a voluntary statement to the police depends not only upon his age but on a combination of factors such as intelligence, education, experience, and his ability to comprehend the meaning and effect of his statement. The court also stated that, 'if the minor is mentally retarded or of subnormal intelligence for his age . . . that is a factor weighing heavily against a finding of capacity.' (At p. 385, 62 Cal.Rptr. at p. 600, 432 P.2d at p. 216.)