I’m probably just a couple of years older than you are (late sixties here), and if I’m lucky I’m working out 2-3x weekly. But I’ve got other health issues, one has me on meds that can cause muscle deterioration as a side effect so my physician does full blood work quarterly to look at everything and make sure it’s all stable. So far no prob (thankfully).
Anyway, point is there could be ways to see what’s going on. At the very least you can monitor calcium levels, maybe get a bone density scan to put that hip concern to rest.
Also, do you supplement? I do a lot of those, some for joints and some for metabolism (CoQ10, PQQ), and I can feel the effects if I start skipping those. Thanks for reminding me that I need to add calcium back into those. Had been taking it and forgot to refill when I ran out.
Best wishes! Keep taking care of yourself!