Too young for Music

My son Smayan aged 4 1/2 who is in pre-school is a pretty active boy. But he is on the shorter side when it comes to his height. Anybody who sees him would think he's still 3 yrs old. Actually I myself treat him as a 3 year-old. He is pretty smart boy though. One day he came home from school asking if he can enroll in piano classes. I didn't even think he knew an instument like that existed. I just ignored him but he was very persistant asking me every day if I got him enrolled in the class at his school. That made me start thinking how young is too young for a kid to learn music. I googled and started reading everything I could find about this topic but then I realised that unless I try it out I will never know. Maybe, I have a child prodigy waiting to be discovered on my hands.