Whoever told you that mastubation causes prostate cancer!!? It is absolutely baseless
Prostate cancer is rare in males below 40 and that is the age you should start screening.
There are other risk factors for prostate cancer such as increasing age, African American race, positive family history and men with certain genetic disorders such as Lynch syndrome.
Next Steps
You can start screening once you are 40. Till then, there is no need to worry.
Health Tips
Avoid smoking, fatty foods and do moderate exercise