One very common thing I've heard when a transman comes out is "I look back at my childhood and so many things make sense now". They then go on to bring up examples of times they wanted to be a boy and activities they engaged in that were considered "boyish". These memories are then used to prove that the person did experience "dysphoria" as a child and on some level always wanted to be a boy. There are many problems with this logic!
It is very very common for a child to have times where they desire to be the opposite sex. Think about it. A little girl watches her brother play baseball and do all these other fun boyish things. She thinks they look fun and would like to participate....but the message she gets from society and maybe her parents is that these are "boy" things and she shouldn't want to do them. The little girl then wishes she were a boy so she could do these fun things her brother gets to do. She really doesn't have a problem with being a girl and is not experiencing any form of dysphoria. What she is having a problem with is the way society has defined her gender role.
When I came out to people as FTM is was very common for the person I was coming out to to say things like "I've thought about this before, or when I was a little girl I remember Thinking I wanted to be a boy". These feelings are very very normal for people who are typically gendered. A lot of it has to do with the male dominated society we live in and the negative impact this has on little girls.
The 2 people I know that I think are truly trans had very different childhood memories. They talk, not about WANTING to be a little boy, but about how they WERE a little boy. They talk about deep feelings of hatred toward their body parts and extreme depression over having these parts. They didn't have to wait to meet someone that was trans before they realized it....they always knew they were transgender. And knowing this about themselves caused conflict in their life from a very early age.