There is no hard set and fast rule. I think it totally depends on the particular circumstances. Take a long hard look at them.
If the child has no idea what they want out of life–never have, even well into their 30’s–have had trouble being responsible, trouble holding down jobs, have no desire for schooling, moved around constantly, and they go to parties, hang out with indecent frriends, I would say absolutely NOT. Let them grow up, figure it out on their own, finally. They have had more than a decade to do so, if they haven’t by now–it’s their choice, and they must learn sooner or later.
If it’s merely a “transition” stage in their life, for whatever reason, that they have always been very responsible, by all means, be helpful the best you can! Love 'em and help them get back on their feet, because on THEIR feet they must remain.
I have unfortunately witnessed all too many completely irresponsible young adults well into their 30’s-50’s with totally enabling parents, who keep them from maturing, just let them keep returning home at the drop of a pin, the parents pay their bills, etc., kids merely shirk their responsibilities, etc., etc. So I, perhaps more than others who have posted, have seen the damage it does to young adults to be dependent on their parents well into adulthood, when the contrary, kids have had to be out on their own, as early as 18, they find jobs, they learn the value of a dollar, they have to examine their future, it’s a good thing in my opinion, as life isn’t easy. You have to be responsible. The quicker they learn this lesson, the better. I would be very hesitant at this arrangement friend, sometimes love has to be “tough”. Even though it might be hard, to do the RIGHT thing is always a hard lesson. I’m a parent, and I fully know.
May God Give You Wisdom~~
God Bless~~