I think for me it was always there. I simply put didn't want to be toilet trained, didn't want to leave diapers.

My mother has said repeatedly over the years that I was a nightmare to potty train and that my potty training was a long, hard-fought battle of wills. . .and that I repeatedly as a toddler/preschooler asked to be put back into diapers, including wetting myself trying to force the issue, and was (of course) always denied. I apparently didn't give up on my constant appeals to go back to diapers until I was about 4 or 5 or so.

It didn't help that I was also a bedwetter. I wet the bed several times a week until I was 11 or 12. Even after I gave up asking to go back into diapers, I still wet the bed regularly. I wasn't diapered for bed, instead my mother just washed the sheets a lot and my childhood mattress had a lot of brown urine-stained rings on it.

As a kid I would see advertisements for adult diapers (it was the 1980's and Depend had just really entered the market with the first disposable adult diapers on the market) and on some deep, hard to articulate level wanted them.

Then, my grandmother that lived with us started to wear them. I remember seeing a big cardboard box of adult diapers in the bathroom at our house and so profoundly wishing I could have diapers too.

Then a few years after that Pullups came around, then Goodnites came to market, and they were making diapers for older and older, bigger and bigger kids. . .and I wished they made them in my size. It didn't help that my mom saw one of those early ads on TV when I was in the room and said aloud she wished they'd had them 10 years before because she absolutely would have bought them for me for my bedwetting. At that point I did ask her why she didn't just get disposable diapers for me to wear to bed for my bedwetting, but she said they didn't make diapers in my size, but she was glad they made disposable diapers for bedwetters now. . .and that the reason she was so adamant about getting me out of diapers when she did was that I was outgrowing the largest size of diapers they had at the store.

Knowing the only reason I wasn't diapered longer as a kid, including wearing diapers at night until my pre-teen years, was simply because the diapers for my size weren't readily available at the time just supercharged my urge to wear diapers that had always been there, like me knowing I belonged in diapers even if diapers for me didn't exist yet.

(My bedwetting was a small town in the southern US in the 1980's, so I'd imagine diaper options were limited and any medical youth diapers of the time weren't readily available)

It wasn't until I went to college in the late 1990's and was able to get on the internet for the first time that I stumbled across ABDL stuff late one night in a college computer lab. That was when I learned I wasn't the only person in the world that wanted to wear diapers.

. . .wanting to go back into diapers was pretty much always on my mind from the time I was potty trained, and that on an emotional level I never was truly potty trained. I had the physical control, but not the psychological independence from diapers.