Didn't have to be convinced because obsessed by the Earth shape since I am young. As far I can remember, it became more obvious when at 10, I received a globe for a birthday and so, had the time to work on it at home instead of some free minutes at school.
Shortly, I had the feeling that something was wrong between the pictures I saw on my school books and their representation on the globe.
At 16, I went to a balloon summer camp and what I saw just confirmed my doubts.
Born in end of July, I was always celebrated with some "moon landing birthday cards" so the space missions interested me a lot and... again, I was doubting... So with the years, I bought a lot of telescopes, walked the French Alps to be high enough trying to find some evidence.
Recently (perhaps December 2016), by chance, I saw that some people were thinking exactly as I am and started to study what information they share. I can not say that I am convinced, I only say that the Earth is probably not what we were told it is.