I agree, sounds like he's an adult and it's his business. BUT does he live with your mother and use her computer? In that case, I wouldn't let him use the computer if I were her (but she needs to set those rules if she wants). He can go to the public library to study for the GED, or even better, go to the computer lab at the local community college that teaches GED courses. My mom teaches GED at the community college, and many students do not have computers at home so they study there.

The GED is all computerized these days, so students do need to take practice tests on the computer.