Translation:He is too young to use the Internet.
In American English, THE is required for this sentence because you are referring to the internet. There are instances like internet shopping (browsing, trolling, etc) for example that you wouldn't use the, but that is because you are talking about the action of shopping and not the internet. Examples: He is too young for the internet. He is too young for internet shopping. He is too young for shopping on the internet.