I suspect my experience may differ from others here, as I find that with increasing years my voice has actually got higher. I think this is to do with gradually losing my lowest notes, and therefore tending to sing in higher keys than before. But I find I like this much more than I ever liked the lower keys. There's something quite thrilling, quite exhilarating about pushing yourself to the top of your range; and it seems to me that many of the songs I sing have their emotional nucleus at the top end of their melodies. I have a fairly high speaking voice, so maybe I was always destined to sing "up a-height", as we used to say in my home town.
And perhaps unsurprisingly, my favourite singers have tended to be those with plenty of altitude.
Anyone had a similar experience?