Toenails actually grow more slowly as we age, because of reduced circulation but years of toenails rubbing against shoes can make them harder and thicker, making them difficult to cut and shape.
The condition even has a name, onychogryphosis, which is not only unsightly, but also painful when pressing against shoes.
Action: Soak feet first to make nails softer. Use nail clippers on thick nails, as these are sharper than scissors, but if nails are still too difficult to cut you may need to see a podiatrist to have them trimmed with an electronic file. If you can trim yourself always cut the nail straight across following the natural shape of the nail and avoid trimming too close to the skin or yanking at hangnails.