Bob & Johnny - Your voice will change, certainly (Hey! I'm only... errrrmmmm... 30-summik...). It won't get stronger by virtue of age, though. Ultimately, even with professional know-how, control & volume will weaken. Professionals are professionals for a reason. Not all of their techniques will be applicable (you ain't trying to sing opera, for a start!). Nevertheless, they have many good practices (& many good practice routines) that will help preserve the voice.

They're offering the distilled wisdom of many centuries remember... ;)