I realised I was gay around 14-15, but when I was around 12, my middle brother who is 11 years older came out as well, so I had a concept and understanding of it, and then when I was 16 my Uncle came out as well, the gay gene is strong in my family it seems xD
But I only came out August last year (22 then), I wasn't like keeping it hidden from any particular reason by that time, I had just gotten used to keeping it hidden due to how bad high school was and College was just meh and the people I knew I didn't feel they deserved to know me in full, as to why I kept it from my family until I was 22, I honestly couldn't say.
My middle brother had "seen" the signs when I realised it myself at 15, but never brought it up until I was ready but he had found I had an account on a site he was apart of and I wasn't aware he was on there, he comes to visit one day, walks into my room, sits on my bed and stares at me with a deadpan expression for like a whole minute. "Is there something you want to tell me?" his expression doesn't change, I stare blankly wondering what the hell he's going on about, then he breaks into a cheeky grin and says the site's name.
I immediately turn bright red, he still let me tell the rest of my family in my own time, I prepare, go downstairs, pause the TV my parents are watching, I sit down and tell them and they just stare point blank "Oh? Okay then, we still love you." and I'm like thats it? I ask them "So you've never thought about it, never assumed or anything?" and without a beat they go "Why would it matter to us? as long as you're happy, we are happy."
and the rest they say, is history.