left at 17? What? Like you you literally left home before being 18?
I don't even understand how you can leave home at 17. Obviously the school system and society must be different. Here in Italy: until 19 years old for most people, including me, but then there are a few who might lose a year and finish at 20 years (and there were 1 or 2 people like this out of 20 people in my class so they finished at 20 even though it's rare) you are in high school; during this time have to be in school roughly 5 hours/day Mon-Sat, plus on afternoon you have roughly 2-3 hours per day of homework (and in the 6-8 weeks prior to the final high school exams in summer, when you are 19, you easily have to study and prepare for 30 hours per week making it nearly impossible to work in the mean time). Work might be possible on the last year of school (and before the preparation period for the final high school exam in summer) when you are 18-19, maybe 4-5 hours per week I guess, but what job would you do since you could devote 4-5 hours per week and stop in early summer-late spring for the final high school exam)? It would have to be something on the evenings or only weekends (and it would be hard because you have homeworks also on weekends).
When I was at school, for example the school wouldn't even let me leave school without a parent's permission even if I just was 18 years old (even 19 for what matters; but they asked the same to the 20 years old who missed a year). There were a lot of debate and most schools didn't allow for example children to sign themselves even if they had 18 years; they still neded parents' signature for everything (leaving early, skipping school day and so on) even if 18, because from their giuridical point of view the school's responsibility towards parents who entrust their children to a school, trumped the fact of being above age according to law. At least this was the case until 13 years ago (when I finished high school), don't know if things changed. I have sources, but they are in italian so it would be useless to post them here, and quite off topic (since they are specific to italy and it's clear 90% of users here are from usa or english-speaking countries).
Here they won't let you rent a place until 18, and I can ensure that 90% of places will never let you rent a place on your own, if you are so young, without a written warranty from parents (which they must sign in person and means that they will pay for you in case you don't and is a legal document). At best you might find rooms in shared flats when you are 19-20, but I don't know of any homeowner that would rent you at a 19 years old without a warranty document (guaranteing they will pay for you in case you are late) from a parent with a permanent job.
Also in italy for example there have been a few judge sentences (i remember reading on the newspaper two different cases about this) over the last few years, where parents are responsible until the son has reached economical independence. So they literally can't forcefully kick their kid out until he has reached economical independence or prove that they willfully refuse jobs that would otherwise fit their attitudes/aspirations. Personally I agree with those judges because parenting and caring about children never stops and 18 is not a magical number, but I understand that we are in a different culture, so I wont' argue about this anymore. We have different opinions.
Anyway I don't even know of any 18-20 years old with a stable job (which would earn enough to pay rent). The only 20 year old that work full time I know earns 600-700 euro, which would barely be enough for renting a single room (not a flat) in city center and bills (but this does exclude all other expenses like food and so on). And I'm sorry I understand sharing bathrooms and kitchen when I'm a student, but not sharing when I work full time. If I have to work full time, I prefer staying 5-6 years more in my parent's home while working until I can afford a place on my own. The only time you should be sharing kitchen and bathrooms with 4-5 strangers is when you are away in another city for uni; no sense sharing a flat if I can stay with my parents (and don't plan to change city) for 5-6 years just until I can afford a whole house or flat on my own.
It's what everyone does here, and a good parent should want the best for their children even if above age, which means enjoying their sons for just 4-5 more years in their house (if they can afford obviously) so that the children can afford a house on their own in the future (unless he wants to move out of his own choice early) and maybe save something for retirement so they won't live in poverty.
P.S.: in italy just to give an exmaple of how you don't stop being dependent on your family at 18, sons/daughters (of any age) can be dependent for tax reasons to their parents at any age (as long as they earn under a treshold amount) and parents get a lot of discounts on their taxes (not sure how to translate the correct italian term in english sorry). I know a 35 year old person who lives with their mother and the mother enjoy a tax benefit (and it's not small) from it, because he earns under that threshold. I also don't know any person under 25 years old who isn't dependant on their parent on their tax declaration (and this also if they live outside their parent's home during uni). Most people start earn enough to not be dependent for the tax declaration in their late 20s.