If you are 60 or over, you are more likely to get PD. Seventy-five percent of all cases of PD begin after age 60, and incidence increases every decade after that up to about 80 years of age. If you do not have PD by age 80, your chances of getting it are small and are substantially lower than when they were when you were 60 or 70.
Most people develop initial symptoms of PD in middle age. Although dopamine declines in PD with age, research is beginning to support the idea that Parkinson's affects many aspects of the nervous system.
Stewart A Factor, DO and William J Weiner, MD. (eds) Parkinson’s Disease: Diagnosis and Clinical Management: Second Edition Edited by 2008 Demos Medical Publishing.