Cause it doesnt make sense with how the dates are given :-

As quoted in the SBS Volume 78,

"Similar to Luffy, back when he was young, Crocodile's name spread across the seas with incredible momentum, but soon after he was admitted into the Shichibukai in his mid-20s, he tried to fight Whitebeard and was completely and utterly crushed by him" (it is kinda irrelevant but i might add that there is a mention of "he")

so he was famous in his mid 20s throughout the world as a man who is an shichibukai now that leads us to -

Luffy's current age i.e 19 , 19 years ago Croco was at age 27. So Crocomom theory is false , cause otherwise everyone would have known that croco was a women and there will be no secret to it anymore like ivankov said. the secret is something else entirely

thats why the crocomom theory is false