No, nine is not too young to discuss masturbation with children in an age appropriate way. Masturbation is a natural behaviour, and by nine most kids would have discovered touching their genitals is pleasurable, even if most are not actually masturbating. I recall having a conversation with my son about it at a very young age. As I recall it was something like I knew it felt nice to touch his penis, and it was fine for him to do that, but it was something to do in his private time, not when other people were there. At nine I’d be happy to have a more in-depth conversation about what masturbation is and why most healthy people do it at least at some point in their life. Making masturbation a taboo topic, is not a wise thing to do.