Tom was riding his skateboard down the sidewalk.
Do you also know Tom?  How did you know what he was doing?
I saw him outside from the window.
Tom is pretty good at skateboard riding. I used to do it as a kid, but I've forgotten how at this point in my life.
This is why kids should do shit while they're young.
You're right about that.  Childhood is a time to have fun and explore our hobbies, even as we work to learn about the world.  It is good that Tom has found something that interests him so much.