I kinda knew I didn't vibe with my AGAB at a pretty young age, maybe 12 or earlier? Idk i just kinda remember vague disassociation towards my agab. One of the first concrete trans thoughts i had was while watching an anime where full body cyborgs exist and I remember thinking/wishing for that to be real so I could swap into a woman's body. The same show also made me aware that being attracted to the same/both genders was a thing that could exist.
At the time I didn't really have the knowledge to really grasp the ideas that were forming so I didn't accept/understand I was bisexual until I was maybe 20. And I didn't really come to understand this general disdain for my physical and social gender and sex were a symptom of being trans until about mid 2019, or when I was about 24. The weird thing was that I knew and understood trans women specifically because i'd befriended a few over online MMOs (and asked the mandatory prying questions that apathetic teenagers tend to ask. thank you so much for your patience Kira/Demi.) but didn't associate the status with my own situation.
Figuring ourselves out is a hell of a path and nobody's is identical to anothers, so don't feel too overwhelmed with your current situation or the possibility of being a late bloomer, things fall into place eventually.