First let me share my personal experience. You may have difficulty believing what I am about to tell you because it is not what you generally observe as singers age. My voice has actually continued to improve throughout my more than forty years as a performing singer. Within the first year after completing my initial research on the voice in 1977 and applying to myself the fundamentals of my evolving voice training method, my range expanded to over four strong continuous octaves. And yes, this included the disappearance of any register break or weak upper register.
This spectacular result confirmed the validity of the vocal principles I had discovered. These principles became the basis of my method when other singers I coached achieved similar results. Since that time my voice has remained full, powerful, flexible and versatile. I am able to sing for hours at a time with no fatigue or blow-out. To the contrary, the more I sing the better my voice becomes. I am continually surprised by the development of new colors and variations in my voice. With each passing year it becomes more expressive than it ever was.
The voice continues to be a living and growing instrument when it is correctly treated and properly exercised. Obviously and unfortunately this is not the experience of many singers. To keep your voice performing at its best year after year, you need to know what affects it adversely and how to properly maintain it. This is why it is vital to become educated about your voice and what influences it. You can only make correct decisions and take action to foster your vocal growth when you have true data. Knowledge is power.