I agree he is too young to learn astrophysics and all that. However, you can teach him about space in a manner which he’ll enjoy and understand. For instance there’s Space Camp in India. They take kids to the US Space and Rocket Centre at Huntsville. There they are given hands-on astronaut training. They are also taught basic mathematics and physics related to the space. I think your kid will love the experience and this will also help him gain confidence and conviction for his future.