The incidence of Parkinson’s disease rapidly increases over the age of 60 years–with only 4% of cases occurring under the age of 50.
Van Den Eeden, Stephen K., Caroline M. Tanner, Allan L. Bernstein, Robin D. Fross, Amethyst Leimpeter, Daniel A. Bloch, and Lorene M. Nelson. Incidence of Parkinson’s Disease: Variation by age, gender, and race/ethnicity. Am J Epidemiol. 2003; 157(11): 1015-22. http://aje.oxfordjournals.org/cgi/content/full/157/11/1015