Yeah... I understand what you mean. I've pretty much been mortified of aging ever since the age of 13 or so, when I realized that eventually getting older didn't mean just being taller than my mom anymore, it meant that my voice was going to change. And then aging meant every single year getting more and more masculine, every single year losing more and more hair, every single year getting more and more away from that ideal "cute" image of myself that I had in my head, and looking more like a big dumb guy.
Now, while that fear has diminished since starting transition, because, yes, it is MUCH happier thinking that I'm going to grow up into a woman, and I'm not going to lose any more hair, and I'm not going to keep growing more body hair everywhere, and that as I get older I'm going to become more and more feminine, I'm still afraid of aging. And the reason is, because I've always wanted to be a cute young girl. And now for the first time, I'm starting to be able to see her. And yet, because I'm 27 years old, I know that this is not going to last very long. Unfortunately, by the time I've been on hormones long enough for them to have fully feminized me, I'll be pushing 30... and, well, that tends to be the traditional border between cute girlhood and serious adulthood. And I'm still not ready to be an adult yet. Honestly, in my mind, I'm still a kid. And I'm not ready to grow up yet. I want to be a girl first before I become a woman, and, well, because of the age at which I started transition, that is going to be a VERY narrow window where I'll be able to. So yeah, I am still afraid of aging. There's so much I still want to experience while I'm young. I do want to feminize more, but I wish there was some way that I could just stay 27 while it's happening rather than having to wait until I'm 29 or 30 for it to be over. 30 just feels like such a looming milestone that I'm terrified to have to cross.