I left out of the blue at 23yo while auxiliary pioneering because I was unhappy, I was realising that my personal morals were not those of the JWs and that I didn't really 'like' Jehovah, his organisation, or most JWs! I am actually ashamed that it took me so long for me to want to get out, and that I wasn't bright enough to really question anything prior to leaving.
After some months I disassociated myself in a letter to the congregation a) to stop elders harassing me and b) to show young Witnesses that some people do actually leave the organisation of their own accord and not just because they want to have sex!