Do you think the American tradition of 18 year olds leaving home to live independently contributed to the country’s great economic growth?

I think the opposite is true. The fact that kids COULD leave the home and live independently resulted from the great economy.

Look who I’m in agreement with!

Actually, it might be most accurate to say both are true, in a cycle.

Chicken or egg thing?

No. I think both aspects further each other, something like the child activity of leapfrog.
A strong economy can support a high volume of new young adults, and in turn the addition of the new youth, strength, innovation, allows for higher economic growth.

No. 18 year olds probably left home to get away from the drudgery of Father’s farm chores, Mom’s household chores, and sibling crap.

No, I don’t think so. If you look back through history children went into the workforce at a much earlier age, sometimes before the age of 10. Attending school until 18 and then entering the workforce full time is a recent phenomenon. I think a more likely factor was the labor force demanding, and getting, wages that were above the bare subsistence level preferred by the capitalist system. Unions and other groups that gave workers a way to exert pressure upon their employers and affect their bottom line through strikes, walkouts and such probably did more toward the improvement of the economic environment than 18 year old employees.
What we have seen since the late ‘70’s has been a concerted effort on the part of owners, stockholders and politicians to quash the unions that exist an keep employees from any efforts to organize themselves to reemphasize profits over people. This is why we see a weaker economy with falling or stagnant wages in these times.