I've been doing fanish stuff almost as long as I can remember but it's only in the last several years I've started to think of myself as someone who's part of fandom and even then it's with caveats about which part of fandom. (Ie SFF book fandom but not really transformative works fandom.) It might be more straight forward to talk about weather I consider myself a fan, but it's not so much about my identity as someone who likes stuff I've always felt comfortable saying I'm a fan in that sense it's more about my sense of belonging to a community.
As kid I used to play pretend games based on my favorite books, have long philosophical arguments with my friends about what book characters should do and just generally obsess of my favorite fictional things. At one point I had a handmade spreadsheet of ElfQuest characters. All of that made me a fan, but since I was mostly doing it by myself it didn’t make me part of fandom.
I first encountered the idea of fandom as teen reading author personal essays about going to cons, voting in the Hugos and doing SWFA stuff. Some of them even talked about writing fanfic. The library had a several collections of Hugo winning stories with commentary by Asimov where he wrote very affectionately about cons and such. (I didn't learn about him assaulting women at cons until years later.) So I knew as a teen that SFF fandom existed but it didn't feel like something I could be part of. It seemed like something you had to go cons to do, and that was pretty scary for me back then.
This was also around this time that my family got home internet access. I was soon joining forums and mailing lists to talk to other people about books on the internet. This would have been in the early 2000s. But at the time I didn’t really think about what I was doing online as fandom that still seemed like something that happened in person.
I’m not sure when exactly I started thinking of myself as part of fandom. Not for a long time after I’d be active in online fandom. Maybe after I started voting in Hugo Awards? When I started writing short fiction recs regularly, which happened soon after? When I started writing for ladybusiness
? Maybe not until I started going to conventions. I can’t recall a moment when I suddenly thought well I’m in fandom now. Looking back it's a bit sad that I struggled with this so much.
I had imposter syndrome about belonging to fandom. Like me now would definitely tell my teen self that she was part of fandom. But always felt like I was just on the edges of that space.
Right now I’m pretty happy with my place in fandom. I have friends to squee about lovely media with. People read things I rec and enjoy them and that makes me happy. I go to cons and enjoy them. I write a regularly for a Hugo Award winning blog! But all that is because of network I’ve been building up slowly over a long time.
When communities are amorphous and have ill defined boundaries it can be hard to feel like you belong. And when you take part in fandom online but don't go to cons or write fic it can feel like fandom isn't aimed at you. Community is hard. I still sometimes feel like I’m just shouting into the void. Feeling like you belong can be elusive. I want everyone to have fun enjoying media and talking about it with other people, but I’m not really sure how to use my experiences to make people feel included.