What information can my adopted child get about bio family?

My husband and I adopted a son and he is now 12 years old. He has been asking about his biological family, especially his mother and father. We have told him everything we know about them, which is very little. We live in Los Angeles, under California law does he have the right to get information about his biological family? We want to support him in this and believe that at the very least, it would be good for him to know his medical history. If he is allowed to obtain this information, how do we go about helping him get it? Does his age matter such that if he can’t obtain it now, could he access it when he turns 18 or 21?