So my daughter is 12, and her room is always messy. It drives me bonkers, and I'm constantly biting my tongue about it!
So, at 12 what is reasonable? I generally just shut the door to her room and walk on past, because the mess bothers me. Consequently the floor is rarely hoovered and the room rarely cleaned. She also loses/damages (her own) possessions as a result of the mess (e.g. losing one glove, facewash spilt on a book, accidentally sits on and snaps ruler etc). When this happens she either goes without, or replaces items with her own money.
She's not allowed food or drink in her room (apart from water bottle) because of the mess.
Her floor is generally clear in the middle, but mess and clutter round the edges of the room and on every surface, bed rarely made, and often has stuff (books, clothes etc) in it. She'll empty the bin or go and get washing when prompted and will strip and change the bed when asked. She'll shuffle round and tidy up a bit if pressed, but honestly not to what I would consider an acceptable standard.
Her room is a good size 13'x11' although the clutter makes it look small. Her brother is in the 6' x 6' box room by luck of birth order. His room is cluttered, but kept tidier than his sister's.
She's a great girl, polite, well behaved, achieving highly at school. She's busy with lots of extra curriculars and puts loads of effort into her school work. Do I let this slide? Is this level of mess acceptable for a 12 year old? I appreciate it could be far worse!