Kind of. I'm 21 and I don't believe my feelings will ever change, but I do worry that transitioning may not be right for me. Kind of an "Oh, no, that stuff only happens to other people!" thing. I wonder if it would be easier to just stay as I am, and be a tomboy. It would be much easier socially, since that sort of thing is widely accepted, but I know I wouldn't be happy. I don't want to feel uncomfortable in my own body, or be called "miss," "ma'am," and "young lady" for the rest of my life. So, I guess I kind of am afraid it's a phase, and that I'll wake up one day and say "Oh, never mind, I'm actually just a tomboy!" That's what really scares me.
Don't worry about what age you realized, either. There's no special age requirement! For myself, since I learned the term 'transgender,' did my research, and got the guts to go see a therapist, I've been able to make sense of a lot of things I didn't understand about myself before. I learned it when I was 19, and I still come to realizations about why I felt a certain way, or said a particular thing all those years ago. Just take it easy and go with it. Any path you take is the right one, as long as it's what you want, and it may take several before you find the understanding you're looking for.