You call an eighteen-year-old boy a boy? In my country, these guys are already going to serve in the army. Where is childhood here? These are adults and already sexually mature people who must understand that upon reaching adulthood, a person bears full responsibility for each of their actions.....
Yes! A thief at age 18 is no child, those bad directions have been forming for some time and are not new thoughts. That kid needs to be forced to face reality, perhaps even go to jail for a while, or he will be at risk of always being a criminal.
18 is still young, they could do stupid things as minds not fully matured we all go to these same phase in life. But this one seem trying to impress his father like he can get make money online by defrauding.
I'm not sure if I could really confront the father about it but I would probably tell the kid to tell the truth himself to his father before he learns it in a very cruel manner. But if it works for OP, I guess its his way.