I understand that two of the "hallmark" symptoms of PD are slowness and stiffness. Of course these symptoms are also common to aging. What characteristics are there to PD induced slowness and stiffness that are different than those of normal aging?
Certainly if one is slower/stiffer on one side significantly more than the other, then that is abnormal and maybe representative of PD rather than normal aging.
If the slowness and stiffness is accompanied by tremor at rest, then it is probably PD.
If the stiffness and slowness is accompanied by other signs such as soft voice, shuffling gait, decreased eye blink, decreased facial expression, slow and small handwriting, difficulty getting up from a low seat, decrease in arm swing when walking, stooped posture, then these all point to PD rather than normal aging.
If the symptoms a gradually getting worse over time, then it may be more than normal aging.