My thyroid function seeems to have gone with a few other things, according to my last blood test a few yrs. ago. I experience many of the symptoms you described. I do believe it is an aging problem. I’m one of those people who doesn’t believe in taking medication as the side effects can be worse than the cure. I was prescribed synthroid (levothyroxine sodium tablets) for the thyroid.
Many friends are on these pills. I don’t take them -it has to be adjusted through blood tests.
I try to eat natural foods, take liquid vitamin D and drink a few Tblp of mineral oil or sunflower oil periodically to help.