In case of Parkinson’s disease, the section of human brain that controls the movement of human body gets affected. Its symptoms can be seen after a long time, not instant or at initial stage. People suffering with this disease over a long period can have tremble in their hand and affect their lifestyle like how they talk, walk, sleep and think. Parkinson’s disease mainly affects older people like 60-year old or above 60. That doesn’t mean younger is safe from this disease. Sometimes they are also affected by Parkinson’s disease, but the chances are very low.
Source: https://www.webmd.com/parkinsons-disease/parkinsons-disease-overview#1