Lol, cracking doesn't last that long, only a few months
My voice was really bad when I was 12, and now I'm 14 and there's only a few times that it cracks monthly, although I'm pretty sure it's not done yet. Like I said, it really all depends. Hormones are what cause your body to grow, and when to do a lot daily things...and those doctors who specialize in the study of hormones get paid a lot
Nobody can really tell you when anything for you will happen, so I don't know when your voice will drop fully.