Wow that's a question I haven't thought about in years. I started drawing babyfurs, as I recall, in 6th grade. I copied the styles of Toddlergirl/Babystar & TaviMunk especially closely back then lol. Once I turned 13, I was able to *somehow* convince my mom to allow me access to my own FurAffinity & DeviantART accounts (god how I miss early 2010s FA & DA). I had been mesmerized by Toddlergirl's "Found" comic which was quite new at the time beforehand (around the time I started to draw babyfurs in 6th grade/summer of 7th grade).
My first character, made at age 12, was an orange housecat, named Sarah Katz (while Sarah is my deadname, it is still the name of my OC, Sarah Katz... just don't refer to ME as Sarah, thx). She wore Pull-Ups and was 4ish in my headcanon for a long time. A few years later I aged her up to 6 iirc (kindergarten age anyway) and at that point she didn't wear padding anymore.
The age regression/childish side of me has been a part of my being since around age 9, and I had been drawing anthro characters (furries) since I was a small child. It sorta makes sense that they'd intertwine sooner or later lol.