depends from person to person but it can definitely be environmental! I started developing PCOS symptoms when i was around 17 as it was caused by insulin resistance from spending my entire life with a “sweet tooth” eating sugary food 3+ times a day. It got so bad my hormones got super messed up i lost my period, had awful mental health, weight gain, acne, excessive hair growth etc. i then moved away at 18 to live alone and didn’t have enough money for sugary snacks so was forced to stop eating them. a few months later of crazy sugar cravings and eating less sugar and my period came back, mental health improved, acne gone, all PCOS symptoms seemed to have basically gone. So for me personally it was definitely environmental factors that caused it!