Also for most women it takes a long time to actually get diagnosed and start treatment. So it takes longer and longer to conceive.
And for some (ie, me) the ObGyn provides a sweeping diagnosis of PCOS without a single blood test or ultrasound. The basis for the diagnosis is that my cycle was long and likely anovulatory. She may have been right but she may have been wrong. Either way, I wasn't impressed. I was "diagnosed" 18 months after DS2 arrived and I didn't have too many dramas conceiving either son.

I don't mean to be off topic, it's just that I think PCOS can also be a "convenient" diagnosis for some drs, if that makes sense.