A little less than a year after puberty struck, I started using a masculine variation of my first name, as a nickname. It was difficult to get people to use it, but I stuck with it off and on until I moved out and started working. I tried there as well but people insisted on using my legal name. When I got online, it was my go-to name until the first time I 'outed' myself to people who assumed I was male (a horrible experience, I won't go into it here). I went back to it again once I got away from those people. So when it came time to officially change my name, there was no question as to what I'd be using; it was a name I'd identified with for most of my life, even if other people didn't identify it with ME.
Having people use it now, and having it be my real, true, legal name... it just felt like I was finally being recognized.