I did my best to condense the story and of course there are missing details. I was saved just after my twelfth birthday. I was raised up until that point in a Baptist Church. After I was saved I began attending a Church of God. I was there about 3 years and I studied scripture. I had been raised in church I wasn't completely ignorant of scripture at 12. At 15 I was moved by the Spirit to an Assemblies of God church. Where I was there for a year, stills studying. I had become good friends with the Pastor and we would often have long bible discussions after Sunday services. Some converstations taking place after Sunday Night services which would last until 2am sometimes 3am. I had thorough knowledge of scripture. Not perfect, not expert by any means. However my Pastor, who was a godly man, offered me the position at 16 after months of prayer about the situation. I prayed about it and accepted the position. The class was Wednesday nights prior to Youth Service starting at 4pm and lasting until 6:30pm(usually)The class was not a beginners/new believers class. It was deep study of the scripture aimed towards 19-23 year old college students. Was I taken seriously at first, No. The first class only had about 22 people attending in a medium sized room. In the first month we expanded from 22 people to 78 weekly in attendance and were moved to the Sanctuary due to the lack of room. Some younger than 19 others many were in their mid 20's and some even into their 30's. Yes, I worked in the sound booth in the church. I also Preached 1 Sunday a month under my Pastor. In the 2 and half short years of my attending this church there was a total of somewhere around 108 that were saved under the ministries I was a part of. I am 19, soon to be 20. This was not that long ago, I understand that. However, I have not falsified any information.
I see your problem! I have seen countless pastors take a very young man and begin to mentor him. This means talking privately with him all the time, and giving him opportunities to teach and preach. There is nothing wrong with this. I had my mentors in seminary, because I was in churches which did not ordain women, or let them preach. I respected them, although I did not agree with them.
I also had an excellent mentor when I was a chaplain. He was Lutheran and I was Baptist, but we never had disagreements. Of course, he believed in infant baptism, and I did not. But since it was all extremely old people, it was never an issue (although we did baptize one 92 year old woman in a wheelchair, not by immersion, but that is even ok with Baptists) This chaplain gave me so much insight into ministry, and gave me incredible opportunities, including recommending me for a full time chaplain position within the system of the long term care association he was a member of. I could not take that position, unfortunately due to being very ill at the time.
So I don't think that of yours pastor was thinking how knowledgable you were about the Bible, but rather, that you showed tremendous potential in serving God in the future. There is never a wrong time to start TRAINING young people. I would imagine he kept a close eye on your teaching and preaching, and your doctrine either by himself and/or other mature members of the congregation.
But you do not outline the reasons for which you left that church. Did you initiate it because you did not agree with basic AoG doctrines any more? Or did that pastor ask you to leave, as he saw you teaching false doctrine that was leading people astray? You don't have to answer of course. Charisma does go a long way to explaining why your Bible study expanded, too! If you were interesting and excited about what you were teaching, I think it is wonderful the ministry expanded and people were saved.
But still, this does not make you an expert in the Bible. The proof is in the pudding! You embraced heresy, and that tells me your Bible studies were shallow and without any knowledge of exegesis or Bible interpretation. Let alone wisdom, experience or maturity! Sorry to be so harsh, but when you introduce yourself as a Bible expert who embraced a heresy, and don't understand what your pastor was trying to do, it indicates to me, that as a scholar of the Bible myself, you need to be rebuked, not just your false teaching. I know there are people who disagree with my approach, but I have little tolerance for heresy, especially by one presenting himself as an expert when he has no qualifications, training or experience which comes out in the fact that you led yourself astray.