I think so, plus nowadays with how the financial world is going moving back in with your parents/family is not rare.
I recently moved back in my mother's house, with my husband and 3 kids. My parents are getting divorced and my mom needs help with her bills, and really it helps us out too. The house is big enough for all of us, so it's a win-win.
Anyway, I don't believe in that whole 18th birthday equals I'm going to kick you out thing, it's hard out there. As long as there is some financial cooperation I think living at home is ok.
I think its fine. I moved out the day after I turned 18, I moved in with my boyfriend, but had I not wanted to live with him, I would have stayed at home until I finished college and had saved up some money.
I made the assumption for all my kids they would go to college. I would pay for it, and for their living expenses.
If they choose not to go (my son, oldest, dropped out), they're on their own. If they stay in, and graduate, we help them get set up in life, but do NOT expect them to move back in with us (we encourage going "away" to college, helps with independence).
Once they have a family, they SHOULD be on their own. if they're not we did some serious mistakes as parents.
Btw - even though my son dropped out of college, he now makes about $85K a year, has a nice place in San Diego with his girlfriend and his dog. My 22 year old (who graduated from college in 3 years) moved back to NYC where she went to school, and now shares an apartment with a roommate and works full time, paying all her own way.
But the age of 18 is arbitrary. My youngest is 18, but a senior in high school. She turned 18 in October. She will be going to college in September.
Why in America is it not acceptable to live with family? In many countries you WANT to live with family because it works better as a unit and more productive that way. Yes its good to have your own home but I love having family near. Does it get frustrating, yes but family is very important to have close to me.