Sir masturbation doesn't affect bones .it's a very normal activity.there is no link between masturbation and stiffness or bone pain.it could be due to vitamin d deficiency .you can check your vitamin d levels in your blood and share the report with me

Hello there...., Masturbation now is regarded as a normal, healthy sexual activity that is pleasant, fulfilling, acceptable, and safe. It is a good way to experience sexual pleasure and can be done throughout life. Masturbation is only considered a problem when it inhibits sexual activity with a partner, is done in public, or causes significant distress to the person. It may cause distress if it is done compulsively or interferes with daily life and activities. Consult sex therapist...