Although I know what you're saying, there is nothing dumber to me than the "18 and out" mentality of the older and some new generation parents.
Probably the worst thing you can do for your kid is essentially kick them out at 18, forving them to take out loans to pay for school and probably living. Starting out behind is why Americans have 0 savings and a ton of debt, particularly student loan debt.
Sorry, but colleges are robbing people blind these days. This isn't the 1970s anymore.
People think Disney's prices go up? Go price a 4 year education at a reputable university and compare it to 20 years ago.
Also, kids are stupid. 18 year olds are just not equipped to make a lot of finance/life choices that are necessary without a good parent's oversight. To an 18 year old, a loan isn't real until they realize their History/English/Psychology degree isn't going to get them a job that pays enough to payback $100k in loans.
Of course, as you say, they are stupid, they can afford to be because they have a safety net the size of Texas to save them from harm. As long as the parent "shields" them from the world that they are going to live in for the rest of their existence, they will never learn about it either, but, at some point in time they will have to come face to face with reality. I also have to wonder if what you are saying means an 18 year old back then was not stupid and found a way to figure out what life was all about, without the umbilical cord still attached.
You're right it isn't the 70's anymore. Minimum wage is no longer $1.35 and hour, salaries are no longer $7000. per year. College is expensive, but, the payback is much quicker then in the 70's. I carried a $1000. (that's right, 1K, not a typo) student loan when I graduated and because of what the wage was back then, it took nearly 5 years to pay it off. All things are relative.
The use of the age 18 was general in the time. It, of course, varied based on circumstance. We weren't thrown out on our birthday especially if we went on to college. However, once we reached the point where we could earn our own way, we were expected to do so. My daughters were at home, in a sense, until the graduated from college. And were allowed to stay on until they found employment and don't even think about sitting around all day trying to find yourself. You got out and found yourself out there in the world were you were going to live. Then they were expected to find a way to support themselves.
One felt that we should let her stay there until she had saved enough money to buy her own place, rent free, of course, then I reminded her that I had supported her for all her life and my money was gone. I wasn't going to keep spending every cent I had so she could go out in the world and not know what it was to be independent. I was pushing retirement and broke. When was it my turn to save some money for the future?
One of them used to take hour long showers until she was paying for the water and the electricity to heat it. Then all of a sudden 5 to 10 minutes was all that was needed.
They always knew that if there was a problem that I was there for them, but, not until they took the initiative to be on their own. I was their safety net, not their hammock! When all is said and done the real job of a parent is to teach them how the world works and to make sure that they take that flight into it.