What is a junior license?

I was wondering what a junior license is. And what age you need to be to have it. I live in California. I need a way to get to and from my horses barn like on/in a motorized vehicle. Like a moped or something. Its on all surface streets about 2.5 miles but it's very hot where I live and I can't ride a bike everyday to ride that's just exhausting. Please Help!