I started drawing ever since I could just hold a pen because that's what most kids do I guess, and kept doodling to pass time ever since. I consider the real shift happening at age 12 when I discovered people actually post their art online and there are communities for art!! And there are even things called tablets that let you draw digitally, neat!! I was probably the first one in my entire village who had a tablet so you can only imagine how little digital art was talked about, and it took me a good while to really understand art communities exist and you can post art without being a professional.
I don't really remember what my driving factor was with art but I think it was probably the whole aspect of getting better and being able to draw the things I want to show to others, like my characters. And I guess at age 12 I was also really into the idea of becoming a ~ popular ~ artist but that never happened haha and maybe it's for the better; people who become known when they're very young often end up either getting burned out by the popularity or harassed, so I dodged that bullet for sure.
For writing I wrote here and there mostly for school throughout my elementary school but it was never anything ambitious, just the usual stuff kids do. I wrote a couple of fanfics in Finnish when I was 14 but never posted them outside of this one now dead fan forum and I started writing prose in English when I turned 18, back in 2013! So I haven't actually been writing in English for too long, especially compared to how long I have been drawing. My main motivation to write is to tell stories because I have so much I want to share with people!!! Writing feels like it's the right thing for me and for me that's more than enough reason to keep on doing it.
As for OCs, my first characters I actually called OCs were some canine characters back in id 2007? 2008? And then from there I'd say the first OCs I actually got emotionally invested in appeared in 2010 through an RP where human characters also made their appearance properly.