First time I disagreed with the WT teachings was in the revelation book we studied when I was 9 (1988). There was a bit on conventions in the states that accomplished the prophecy of the trumpets and I felt they were incredibly self-centered and boastful to make a claim like that. Then, as the years progressed, I never fully believed the prophecies based on dates. A lot of people around me got disfellowshipped for that and I perceived it as a weakness to believe the “dates” to the commas and periods.
When I was old enough, I had a conversation with an elder who asked me why I didn't want to be a ministerial servant. I explained that I could not, in good conscience, teach things I doubted. He advised me to "wait on Jehovah". That many things he personally disagreed with were eventually fixed on Jehovah's schedule. In the meantime, people came to the meetings, not to hear what we personally believe but what the faithful slave is teaching. So, when we’re on that podium, we may, from time to time, need the humility to teach things we don’t agree with.
That explanation appeared valid to me, and yet, I could never really shake off the idea that I needed to believe things in order to teach them. So, even though I stayed in for another 15 years or so, I never was able to become a ministerial servant. And as the years went by, I did notice many brothers who were teaching in some capacity or another seemed to be following that advise.
The breaking point was when I was supposed to teach these things to my kids… unable to do that, my family and I faded out.