My ct scan said mediastinum: residual thymic tissue more then expected for patients age. what does this mean?

Thymus: The thymus is an immune system organ that typically shrinks in size from childhood into adulthood with very little residual tissue left. Unless you are having immune system problems, previous radiation therapy to the chest, or a family/personal history of cancer/growths in the chest cavity, this likely is a benign finding with nothing to worry about. Just ensure follow up with your PCP.