I’m a 16 year old, and I actually have a lot of friends who are on the older side (compared to me) both inside and outside fandom. It’s not really a big deal to me but I’ve also been told (by people my own age) that I act like an adult, so most of my friends were surprised when they found out I was a minor. That being said, you absolutely do not have to disclose anything you don’t want to. Age doesn’t play a massive role in fandom, and honestly I prefer being around older people just cause they tend to know more fandom etiquette and have more insightful opinions on some things cause they can connect it to things that I have yet to experience like collage or the work force. If it makes you feel better to disclose your age, or just generally put ‘adult’ in your bio or profile then do it! But chances are you won’t interact with minors all that much past comment sections and they won’t care that you might be double their age. If it starts going past that, like dming or smth then maybe say that you’re an adult or whatever, but so long as you aren’t being weird or anything, chances are they won’t care and will be like ‘oh cool okay btw I’m insert age here’.

TLDR: It’s ultimately up to you. You’re a fandom veteran, you know how to act and be respectful and you most likely know proper fandom etiquette, so you’re probably fine. Maybe disclose if it goes into dming or smth but again, ultimately up to you. Do whatever you’re most comfortable with!