My first time messing a diaper happened when I was only 12. I had gotten a pack of 4T-5T pull-ups from the local store (I was very small for my age and still fit in those), and wanted to try them out. It would be the first time I had ever worn a diaper after being potty trained. My hands were shaking from excitement. I brought the packet with me into the bathroom and locked the door. I removed my pants first, and then my underwear. I then carefully opened the package of pull-ups and removed one, looking it over. It took me a while to figure out which side went forward, but I eventually figured it out, carefully stepped into the leg holes, and pulled the pull-up up to my thighs. I was just a bit too big for them, so it required some effort to slide it up above my butt, but I managed it pretty easily. I had first thought I was only going to wear the pull-up; I had no intention of actually using it. But after a while of me wearing it, I felt a sudden and intense pressure in my gut, reminding me that I had not pooped in 4 days. I panicked a bit, because I didn't know if I actually wanted to use it, but I eventually decided that it was made to be soiled. I tried pushing, but nothing happened. I tried bending over and crouching down slightly, into the classic "messing pose," but still nothing happened. I decided to do one last thing. I got down on all fours, with my head almost touching the ground and my padded bottom high up in the air, and I pushed again... and something happened. I hadn't pooped, but I could feel it coming, it was much closer now. I kept pushing and pushing and pushing for a few minutes with no success, until finally the first log of poop started slowly making it's way into the pull-up. Even more excited now, I kept pushing, and the log eventually came all the way out. The log was so big that I could feel it pressing up against both my butt and my crotch. I could tell there was more, so I pushed harder, and a second log slowly pushed out. This one was much smaller, only making a small bulge on the seat of my pull-up, but it was followed by a wave of loose, mushy poop, which flooded the poor pull-up. I could feel there was more, but with all my pushing I couldn't get it out, so I instead just stayed in that position, padded rear stuck proudly in the air, visibly bulging from the mess it was containing. I eventually started playing around with it, and sat down on it too, which felt awesome. I lost track of time though, and my mother pulled into the driveway while I was sitting on my soiled pull-up. I had to quickly clean myself up, hide the pull-ups and put the messed one in the trash. The whole process took about half an hour, and to make sure nobody discovered the pull-up, I took the trash out. I walked right past my mother with the bag that held the messy pull-up, but she didn't notice. That's one of the biggest messes I've ever had, and to think it happened just about a meter from a perfectly clean toilet... yeah, that was the starting stone of my journey to becoming a 24/7 diaper wearer and user. I'm still not completely 24/7, but I do use my diapers frequently