TLDR:

- It's unrealistic in today's world to say that Under No Circumstances Should Anyone Spend 9 Hours A Day On A Computer.

- His/her lifestyle may be unhealthy, but it's not necessarily the computer usage.

- External social realities may make it difficult or impossible to hang out with friends in real life.

- "Failure to launch" is a real problem. Providing assistance to overcome obstacles is better than judgment and trying to force behavior change.

- An actual "Doesn't want to launch" situation is unlikely. If it appears to be the case, it may be because he/she doesn't have a good enough relationship to feel comfortable discussing his/her actual plans.

- It's possible this is a situation of "I want this, but I don't want to want this." In this case, technical measures may help, but they don't have to be particularly sneaky or hacker-proof.

This sounds like it's written by a boomer or earlier generation. I'm rather surprised it's posted on HN, by someone who is apparently young enough to have been a child in the Internet age.

In case you didn't get the memo, the world has changed. A substantial portion of the population, and a much more substantial proportion of this site's audience, spends the majority of their day on computers and the Internet.

Spending time with your friends often happens on the computer today. In case you haven't noticed, for decades, kids have been losing the ability to meet up in person. Causes include "helicopter parenting," media-fueled concerns about kidnapping, fears of overzealous CPS cracking down on people for letting kids go places on their own, plus the Internet.

The pandemic accelerated this trend a lot, especially for young people, as many schools were online-only for multiple semesters.

The kid in question may not be a social butterfly. It's partly his/her personality and interests -- the local teens may not care about the same things he/she cares about -- and also, some people just end up as social outcasts through no fault of their own -- for example mild undiagnosed Asperger's / ADHD / autism may not be obvious to a person or their family, but it may make them behaviorally different enough to just subliminally "creep people out" and turn others away. The Internet can be a lifeline -- it may be much easier for him/her to find a place among its thousands, perhaps millions, of fractally nested communities based around every conceivable group and interest.

Taking that lifeline away seems like a bad idea.

An 18-year-old is legally an adult. Thinking of him/her as a child, or treating them like one, isn't going to accomplish anything worthwhile.

Computer time isn't the problem. It's his/her free time and spending it how he/she pleases. If he/she was hanging out with friends, and they were playing baseball for 9 hours a day, and you wish they were playing basketball, guess what? You don't get a vote, and you're kinda a jerk if you say "You and your friends have to play basketball. Or else I'll find a way to stop your game."

What may be a problem is failure to launch.

Sit down and ask him/her, "Where do you see yourself in 5 years, or 10 years? What do you need to do to get there? What obstacles are in your way? How can I help?"

If he/she is making progress toward a launch -- has a job and is saving up money, or is currently enrolled or in the process of applying to university -- then how he/she spends free time doesn't matter. Trying to impose limitations will just build resentment, damage the relationship, and possibly psychologically damage the son/daughter (see comment [1] for an example of how bad things can get if you go down this road).

If they want to launch, but they're not making progress, ask them what obstacles they face and then really listen to the answers. In comparison to earlier generations, college is incredibly expensive relative to income. The process for scholarships and financial aid is complicated and confusing. Entry-level job postings may require experience. The application process for all three can be quite intimidating to an inexperienced adult. Not having a car is a crippling logistical challenge in many parts of the US. If they're not used to working, it can be a major life change causing severe anxiety.

Offer help, but don't dismiss their concerns as "making excuses".

If he/she doesn't want to launch, and is planning to live in your basement until keeling over at age 99, that's a different problem -- but I think this is unlikely. (It may take some patience and persistence to break through the shell and get him/her to talk about his/her plans -- I sense this relationship may be strained already.)

If he/she doesn't want to spend so much time on the computer but can't control himself/herself, that's actually a problem where technical measures can help. The key is that he/she agrees (freely, without threats or incentives) to be blocked or limited -- it's a voluntary, self-applied tool to help with self-restraint. The technical measures don't need to be sneaky or utterly hacker-proof; they just need to put some extra steps into the process of screwing around when you shouldn't be. It's fine if he/she knows exactly what mechanism is in place and how to disable it, the point is to add extra steps to give his/her rational brain time to interrupt the monkey brain's "Video games fun!" with "Should I really be doing this right now?"

One simple trick is pomodoro, just have a timer that goes off every so often and reminds you to check the time, and compare what you are doing to what you should be doing.

This kind of self-control and self-discipline is hard to learn -- but this is actually an instance where it's better to be living with parents and unemployed. That way, the parents can help train the person's resistance to the siren call of the Internet, and the consequences of a lapse aren't as dire as losing a job or flunking out of college.

Anyway, the point is that approaching the issue in an adversarial way may motivate him/her to move out, but it's not worth the price -- it'll damage the relationship, and possibly psychologically damage him/her as well.

[1] https://news.ycombinator.com/item?id=32091676