I was a bedwetter, and I wore Pull Ups and later Goodnites to be until I was 11. Partly out of shame, though, I didn't consider my pullups to be diapers.
All this going on, I had a dream when I was about 6 where I wore and used diapers, and it never really left me. I remember being at daycare (where I was one of the oldest kids) and seeing a diaper on the floor in the hallway. I was alone and, for a moment, I was tempted to take it. For the rest of my childhood, once in a while something in a movie or TV show about diapers would catch my interest. I once (I think when I was 8 asked about big kid diapers being mentioned in one cartoon.
The next big developments didn't happen until I was 11-12. First, my parents decided it was time for me to stop wearing Goodnites to bed. I objected at first. On the surface, I said that I was still worried about staying dry, but on the inside I had started to like them. Still, I folded. Then I saw the movie Fairly Oddparents: Channel Chasers came out. In that movie, Timmy is turned into a baby and poops his diaper in two different scenes. That kinda flipped a switch in me and I really started wanting diapers. I still had some leftover Goodnites in my closet, and I started wearing and wetting those in secret. Eventually those got thrown out, which I later regretted.
Over my teenage years I became more active online. I generally didn't have access to diapers, or the money to buy them. But I settled for occasionally peeing or pooping my pants, especially pooping since it was easier to contain without a diaper. I did try the multiple underwear trick, though. When I was 17 I walked over to a nearby CVS and bought a pack of Goodnites. I used those a little bit. But I eventually felt bad about it and so came my first diaper purge. The next time didn't come until I was 20 and in college. I had more independence and there was a CVS nearby, so I would occasionally get Goodnites or the store brand from there. And then the occasional diaper purchase became part of my life, though these often ended in a binge-purge cycle. I think I broke out of that around when the XL Goodnites came out. I started buying the boxes rather than the "jumbo" packs since I was confident enough not to purge, and the cost per pullup was a bit lower. From there I eventually grew to keeping a continuous stash.