When they are considered perfectly capable of supporting themselves but are obviously free loading for as long as possible. Note that children in college should not be just "kicked out" because they will have to divert focus from school and their education can suffer.
When they arent in college and are sitting around getting a free ride. Kids in college deserve a break as long as they are doing well. Ditto with first job so they can save enough money to get an apartment. Set a deadline for that and insist on effort and progress.
It all depends upon the circumstances. My Aunt lived "at home." She had an excellent job, and they always shared expenses. She was eventually able to purchase their home enabling them to have a more comfortable retirement. They also had excellent care and were able to avoid going to nursing homes! Sometimes, parents and children get along wonderfully and the living conditions benefit all. :) Freddy the Freeloader is a different tale.
Believe it or not, but age really has less to do with it than you realize. What is more important ... Is ability.
We as parents, should be preparing our children .. Preparing them to learn all the skills they will eventually need to be able to live on their own. It's called nurturing. Nurturing hones skills that will enable a child to interact in the world. It hones skills that support independence ... Not dependance.
Make no mistake .. Once the child has learned the skills ... There also has to be a component of balance between knowing what to do as well as being able to do it. Self confidence and enthusiasm are also components that play a key role.
A parents job doesn't end when a child finally moves out on their own . There will always be a very definitive role between parent and child. There will always be a need for support .. Not as much financial support as it would be moral support.
I don't believe an adult child should be Kicked Out. I believe when a child is old enough to get a job and able to support themselves, then it's time to move out of their parents house. Maybe around the age of 20 or 21
if their in college dont kick the out yet untill they finish studying or untill they are ready 2 leave the house but have 2 follow your rules afer they are 18 if they dont do as u say kick them out dont let them be lazy