I think it's genuinely very strange and sad when people act as if turning 18 somehow immediately makes people an innate danger to their peers, as if most people don't continue doing the exact same shit they were doing when they were 17. in the US, at least, the majority of people turn 18 while they're still in high school. unless they immediately drop out on their birthday, they still have to go to class and ask for permission to use the bathroom. they likely still live with an adult guardian or guardians, which likely comes with some restrictions on their privacy and mobility. they probably Do Not have a great job, if they have a job at all, or much in the way of savings or financial literacy. they are, crucially, the same person they were at 17 years and 364 days old, just with an additional 24 hours. that's still just some teenager.

it's also very telling to me that this question never seems to come up regarding friendships, likely because "should you stop talking to your 17 year old friends after you turn 18 even though you're all still in English class together" really highlights the inherent absurdity in this line of thinking