" ... i'm at an age now when I'm experiencing more uncomfortable sensations in my legs..
don't know if it's just related to inevitable age & declining fitness;..."

Me too! I woke up one night, a few months back, with the most excruciating pain in my left leg. I've not experienced anything quite so bad since but I seemed to be getting persistent, low-level pain around my knees and sometimes my hips. I read somewhere that as a person gets older his/her walking gait changes. There's a tendency for the feet to sort of splay outwards and that puts a strain on the knees and hips. I looked at my shoes and, sure enough, the outer parts of the heels - towards the back - were very worn. I did a bit of investigation and found that you can buy (over the counter in your local pharmacist) some shoe inserts which correct your gait. I bought some and they seem to be working so far - a lot less leg pain.