At what age does one's singing voice usually reach its final range?

I'm 52, and a funny thing has begun happening to me this year. I've never in my life had a singing voice, but like everyone I enjoy indulging privately- in the shower, in the car, and so on. I've never learned breath control and all the other singing tricks, so I'm under no illusion I'll ever captivate an audience. Still, I've discovered my range is noticeably increasing lately- not upward, but downward into the bass range. I'm now hitting and holding low notes that were never possible for me before.

I'm just curious as to whether this is common or not, and how far I can reasonably expect it to go. I've often thought of such things such as reading for books on tapes- if I can expand upon this development and control it perhaps something would now be possible for me.

It's intriguing.

Note: The only DUer (other than my sister) to actually hear my voice over the phone is CaliforniaPeggy. Perhaps she could be persuaded to expound upon what my speaking voice is like and what it might sound like in a recording, just as a matter of curiosity. No need to worry about my ego, CP- be honest to me. I already know you will be.

As an adolescent, I was a soprano.

From my twenties through my early fifties, I was an alto.

Now over age sixty, I sound best as a tenor.

Oh well--my boobs and my butt are a lot lower too....