As I get older the lower end of my voice is deteriorating. I can still sing as high as I always have but it's my lower range that isn't what it used to be. I also can't seem to make interval jumps like I once did. When I was 47 I was in an accident and had to have surgery. They put a breathing tube in me and after surgery my voice was hoarse. Since then the lower end of my range has been a problem. I haven't heard of voices going higher as you age.