I didn't have time to read this tread in detail, but I think a big reason for that a lot of 20 somethings remain at home for so long is student loan debt. College as a whole has really be oversold to American families as the end all be all of moving up in the world. Meanwhile the cost of an education has skyrocketed while starting salaries in many professions have stagnated. Many young people end up with crippling student debt as a result. Its pretty hard to afford your own place when your paying 700-800 dollars per month or more to service student loan debts.
I attended what is generally considered an pretty elite university (consistantly top 10-12 per US News), and I can't tell you how many classmates I know who decided to pursues lower paying professions (teacher, scientist, engineer, or similar) who have really struggled to stand on there own two feet as a result of oweing 60K, 70K, up to 100K+ for their educations. While a college education still confers to many a huge benefits in terms of lifetime earning power, I would definitly give my kids this advice:
1) Only consider paying full price to attend an elite university if you are committed to a career such as investment banking, management consulting, law, medicine, or a similar field. A degree from an elite school is necessary for entry into these fields (or the graduate schools that will get you into these fields) and salaries are sufficiently high to justify the cost. The average cost of four years tuition at an elite school is ~120,000K (or roughly 1400 per month for 10 years). If your going to pay that much make sure you will be earning six figures within a year or two of graduation. Most careers do not offer that income potential.
2) The quality of education available at top public schools (Berkeley, Michigan, University of Washington - Seattle, University of Wisconson - Madison, etc...) is the equal of that available at any university in the world. If you live in a state with a top public school, and can get in you should not pass up the in-state tuition to pay full price at a private school.
3) If you intend to pursue a low paying career such as teaching, non-profit work, etc... you should be very careful to avoid any and all student debt. A student who wants to be a teacher and who can get into Harvard/Princeton/Yale can easily get a full scholarship to a second tier school. If they are really committed to teaching/non-profit, they should take the scholarship over the Ivy League degree as they will be more likely to stay in the profession without the stress of large student loans.
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4) If you are not a good student, can't score over 1000 on the SAT, or can only get into a diploma mill type school, perhaps you would probaly be significantly better off financially pursuing a skilled trade. 4 years time and 5 figure debt is not worth it to end up making 30K per year as a deadend job cubicle jockey. Harsh I know, but its the truth.
I used my degree to become and engineer. While I don't regret my decision, and enjoyed my career, I am currently headed back to school for an MBA (this time with a large scholarship). The career advancement/income potential for a engineer is just not there for one to live what is generally considered a middle class lifestyle while at the same time dealing with mortgaged sized student loans. Eventually, no matter how much you like your job you will want to start a family, buy a home, etc... Excessive student loans can make that hard to manage.