In my understanding, PD is a point based system disease.
Lets say you need 1000 points to show PD signs and symptoms. It can be as early as 30 to late 90 depending on when you reach that 1000 points.
300 points for genetics
Lets fill other 700 points with all other root causes .
Stressful situations in life: 200 points
Diet and level of physical activities:200 points
Environmental toxins: 200 points
Head trauma: 100 points
We can break these categories to subcategories like for diet and level of physical activity : high sugar diet, sedentary lifestyle, low vitamin d,etc…
As soon as you earn that 1000 points you are in.