I have no problem in cutting my toe nails, but several times a week I put my feet up on something and check that I could if I wanted to reach every toe, then I twist my foot and push my knee out to the side to ensure I can still see the sole of my foot - on the same principle as use it or loose it.
When I first stated to check, one hip joint was more resistant than the other, now they are about the same, both good, that is, not that the other has stiffened up. Even at 70, improvement is possible and I recommend trying for it.