A younger person's voice sounds stronger, perhaps faster, and more "full" in vocal tone. An older person might speak more slowly, perhaps have a "thinner" sort of quality to it. For a very old person - like over 80, not over 50 - the voice might be quavering and halting.
Those of us between 50 and 80 no doubt do sound different than what we did when we were young, but I'm not sure I can describe the difference. A man's voice might be more "gravelly," low-pitched and slow. A mature woman's voice sounds more commanding than a younger woman's. (Maybe because of all those years of saying "You kids stop that this minute!!)
A child's voice is usually very high-pitched. A teenager's voice might be deeper, but especially for girls, is likely to have a lot of inflections and verbal habits, like saying "like" or "you know" or having a rising inflection at the end of sentences to make them sound like questions even when they are not really questions. Usually an adult does not have those habits.