I'll echo others here and say that it's funny what people DON'T notice when they see you regularly. I went from an androgynous tenor to a full tenor and then to a light baritone while I was regularly attending my men's group, and nobody seemed to notice nothin'. My voice started cracking before the baritone arrived, so I was careful when I spoke. I never got so much as a raised eyebrow. (My best friend says I sound the same, heh.)
I finally decided to let my facial hair grow out, so now I have a flimsyish beard and an even flimsier mustache. A guy joked about it once in the beginning, but nobody else seemed to see anything weird about it. I guess it helps that I am young-looking for my age, blond (dark blond now), and not otherwise hairy. A scraggly beard on a guy like me excites no comment.
I had top surgery a couple of months after starting this group, and (thanks to good binding) nobody seemed to notice, although I went through a sudden and distinct change in the way I carried myself.
You are young enough to be going through a delayed puberty, so I would sit back and enjoy the ride. If anyone comments on the vocal changes, just say something true like, "Yeah, Finally! I was wondering if it would ever happen!!!" Or you can honestly say that you have been diagnosed with a hormone deficiency or something like that. It's true enough. I expect that few people will say anything, but if you are asked, just say the truth in a way that doesn't out you and is comfortable for you.
I think you would have a lot more issues if you were perceived as female and were going through the changes; I think people are more likely to ask. For example, my mother-in-law thought I had a cold, but she knew me as female and didn't know I was transitioning.