Your Food Isn't What Your Grandfather's Was
Start here, because everything else follows from it.
Your grandfather pulled food out of ground that had not been farmed flat yet. He ate off fields that were rotated, rested, and left alone. Whatever came up out of that dirt came up carrying the trace minerals that were still in it.
Modern farming is very good at one thing: producing volume. It was never designed to keep putting minerals back.
It isn't your age. It's what stopped showing up on your plate.