My Penis is 7.5cm long when erect but I am almost 20 Year old now .

My Penis is 7.5cm long when erect but I am almost 20 Year old now . My penis also doesn't seems to grow longer / bigger in the last 5 years (staying the same 7cm +/- 2cm ) . I started masturbating since 14 year old . I did not pull back my penis forehead in the past while masturbating but only started pulling back my forehead at the age of 16 Y/O . Can not pulling back the penis forehead skin prevent my penis from growing ? Can masturbating 3-4 a week currently do any harm to my penis growth ?

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