Well, I'm 19, almost 20, so I should be done, no? I still sound like a boy/woman (I've heard both), but I'm pretty sure I'm already done with the voice change and everything else that comes with puberty.
And maybe I will. It's just relatively expensive.
Like I said, I would avoid the Finasteride, as it can have some serious side effects. Try Rogaine, that seems to be helping my son, and it's not as expensive.