Question about my voice...?

I would like to know at what age as a male, do I get my "final voice." I believe I started puberty at about thirteen-years old, as my voice cracked at first but changed over that summer, and became extremely deep (almost monotone). Now however, at eighteen, my voice actually seems to have gotten a little lighter, but it still isn't always clear and many times I have to clear my throat. When will my voice finally become stable, or is this it already? And can I do anything to make my voice sound better, like can I mimic a person who's voice I like, and will it gradually change to become similar like theirs? Thank you.