I don’t remember exactly when I stopped believing in God. Having been raised in a fairly open-minded family in Iran, I had no encounter with Islam that mattered until the Islamic movement took power on the back of a defeated revolution in Iran. I was 12 at the time.
I suppose people can go through an entire lifetime without questioning God and a religion that they were born into (out of no choice of their own), especially if it doesn’t have much of a say in their lives. If you live in France or Britain, there may never be a need to renounce God actively or come out as an atheist.
But when the state sends a “Hezbollah” (the generic term for Islamist) to your school to ensure that you don’t mix with your friends who are boys, stops you from swimming, forces you to be veiled, deems males and females separate and unequal, prescribes different books for you and your girlfriends from those read by boys, denies certain fields of study to you because you are female, and starts killing indiscriminately, then you have no choice but to question, discredit and confront it – all of it. And that is what I did.
Fundies might deny it, but in reality fundamentalist Islam, Christianity, Judaism, et al. are more alike then you think. Patriarchal religion has slowed the progress of women’s rights throughout history, and getting rid of it would be a huge step forward.