Arthritis. Most likely there's some arthritis there somewhere. The base of the thumb where it meets the wrist is a very common place for such. The wrist joint itself may have arthritis in it, too. Other things could also cause pain with grip. A cyst or a torn ligament in the wrist. See your doctor and at least get an x-ray.
Pain on grip. I can't say without knowing where the pain is. Grip compresses joint surfaces which if arthritic can cause pain. Tendons at the wrist need to resist deforming forces of grip and if inflamed can cause pain.