It's hard to say, I must've been 7 or 8.
But the basic idea of evolution is not inherently contradictory to a belief in a creator.
The origin of species and the origin of life are different questions.
This used to cause me a great deal of frustration with countless JWs that didn't understand this relatively elementary fact. So many JWs would say, "We don't believe in evolution, you know!"
I'd respond, "Really? You don't think anything ever change? Ever?"
The usual response would be some version of the classic deer-in-the-headlights look.
I was equally frustrated with the WTBTS's books and talks that attempted to reduce the issue to "Creation vs. Evolution" because that also incorrectly framed the issue.
Many times I incorrectly credited the GB with merely stating it the way most people understood it, believing they were smart enough to realize that was incorrect. I now know better. The likes of Stephen Lett, Anthony Morris, Gerrit Lösch and Samuel Herd clearly lack the education and intellect to appreciate the subtle nuances of the issue. Frankly, they're just not that smart.
That being said, it has become abundantly clear to me that, if there is any kind of creative force or intelligence in the universe, it has absolutely NO resemblance to the petty, narcissistic, capricious and genocidal god of the Old Testament.
That god is a psychopath. And all of his followers are delusional, especially the ones that claim(ed) to "speak for him."
The name Jesus comes to mind.