Broody, my dsd is 18 and still comes to us a third of the time, holidays with us, has contact phone calls on set days. She works full time!
I think some step kids find it very difficult to "normalise" growing up and away when it's on a "part time" basis.
Op, I have my own ds who is the same age and I'm also finding him very difficult. I know my dp is really struggling too.
I talk to other parents of boys the same and they all complain about the laziness, rudeness, gaming, moaning and nocturnalness!
I am holding onto the positives that mine does do chores and has done a few hours work for some friends this holiday and is mostly polite if sullen and grumpy. He's also very education focussed.
As the bio parent I have come to realise he is his own person and I might not like a lot of his personality right now, but I can't change him as a person.
I do talk with him and try and understand him, I also lose my temper and shout, I have also removed privileges. I make it clear I have expectations from him and I try and keep them realistic. He's not going to get a job anytime soon (lack of confidence and he's too bloody lazy) but he also doesn't get any money apart from the minimum.
I feel I am genuinely trying and I hope my dp can see that too. Even if things don't seem to change, I am really trying to make things better for all of us.
I know by how my dp treats his kids (ignore all bad behaviour and brush under the carpet) that feeling supported can be half the battle won and makes you feel better even if nothing dramatic changes. It's very hard to put up with bad teen behaviour and have your feelings dismissed. 