Always wanted to be a boy as a kid, tried to fit in as a teen/early 20's, was closeted genderqueer for a few years in there but mostly didn't acknowledge that identity even to myself, met a transman IRL for the first time at 24 and started questioning, identified as genderqueer publicly for a year or so, decided to answer my question at 25. Still haven't gone on HRT, legally changed name or gender, or come out to most of my family.
There are definitely guys on this forum who started younger (teens) as well as older (30s, 40s, 50s, or after significant life experiences like marriage, kids, etc).
There is a lot of stuff in the media lately about trans kids, but there are a LOT of factors that go into being an out trans kid. It requires a highly supportive family, a particularly assertive personality, and access to information (for the kid and/or parents, through internet research, books, education, or other avenues, which can be limited both by socio-economic factors and physical geography). Those kids are unfortunately the exception rather than the rule.
So I'm happy to be where I am now. There are guys in my support group in their 50's and 60's who are just beginning their journeys. And they are happy to finally be where they are.