I had more problems after they finished college. I tried to give them some transition time, to get a job, and find a place to live, because as soon as they reached 21, I felt that my obligation to support, financially, was coming close to finishing up. My youngest started to get in the habit of spending the night at her boyfriends place, then he would drop her off in the morning, where she came in and used the shower, ate breakfast, lunch and dinner and then left again when he was done work.
Not only did it bother me that I felt she was being treated like a girl (of the trade), but, what a racket her boyfriend had going for him. We sat down with her and told her that this was not working for us. We loved her and because of that it really hurt to think she was being used like this. She assured us it was really love. In that case, I said, there should be no problem with you two sharing all day, everyday. If he felt the same, then at least make the commitment to share your lives, either by marriage or cohabitation, but the idea of running back home to Mommy and Daddy in the morning was not working.
She moved out and into his place that week. I was fine with that, in fact, I helped her move. I don't have any desire to make moral judgements about how two adults live their lives and I felt amazingly better not witnessing or being used myself for the purpose of "being handy". They lived together for about 3 years and got married. Eighteen years later (21 total), they are still together and doing well. All of us were a lot happier with those arrangements. (Except MY Mother who was totally flabbergasted about it. Good thing it was my daughter and not hers.)
I still am involved with both my girls when situations arise. It was a difficult thing for all of us, but, in our case I think that it established that I trusted them to take care of their own lives, not be dependent on us forever and trust that I will tell them if I think they are heading in a direction that will be harmful to them. Not my business anymore and I would never interfere without being asked, but, they know I am there to help if I can. So, even though they are both over 40 now, I'm here to tell you that parenting never really ends until you do. I am proud that they feel they can come to me with any problem and that they know, I consider them adult equals. That I will help when needed and not as a limitless safety net.
Young teens, on the other hand, just require, in my mind, a certain degree of responsibility and trust that they will do the right thing. What we have as expectations have a tendency to come true, both good and bad. If we think they will screw up and they know it, there is no reason to be expecting anymore from themselves. If we expect them to achieve good things, they will also expect that of themselves. Individual mileage my vary.