Adult tween/teen life

The prism you may see Age Regression from is one that often is routed in the past and in that past bedrooms were more austere places where you slept and had little over a bookcase or maybe a small radio in them.
Your new-old adult but child  bedroom reflects that life which will include some elements from contemporary teen life such as your cellphone that you use to 'connect' to people and maybe a music playing system.
You can try to keep to traditions routed in your childhood but in the end you co-opt some modern ones simple because in the modern world that's unavoidable.