Does your voice (range) get lower as you age? Is this a fact? If so, does it affect your lower as well as the higher end of the vocal range ( the lower end expands a small bit and some of the upper end notes get harder to hit)? Is this good for bass singers?
One effect of aging is a loss of muscle mass. Since the vocal folds have muscle in them, this can lead to a loss of lower range because a less massive oscillator will oscillate more rapidly. I began to notice this in my early 30s. I did get a slight improvement in my upper range along with it. Practicing, like any exercise, tends to build muscle mass, so reduces the severity of this effect.
Ossification of cartilage and loss of flexibility and elasticity generally also tend to have negative effects on vocal timbre and range, on both ends. Again, practice helps to mitigate these effects.