You will definitely need to wait until your son gets a bit older to learn about cryptocurrency in general. I'll be 30 years old later this year and even I'm still trying to catch the knowledge about it with some confusion in the process.
Comparing video games to make it easier to explain Bitcoin seems like a good mashup. Maybe you can compare it to making cash in Grand Theft Auto 5 and how you become "wealthy" by earning alot and buying things that you want, but when you think about it. Killing people, smuggling drugs, etc for money might not be a good comparison like you can do in that game.
I would recommend first teaching your son on how to save his money and not to splurge on materialistic things like Jordans, Apple Watches, etc. Teach him the value of opening a savings account to grow his money over time.