I'm in good health for my age. a few aches and stiffness in the mornings.'still play tennis and keep physically active..would like advice on diet etc?

Diet: It sounds like you already exercise regularly, so you are already doing well above average. Assuming you don't have any other significant medical conditions such as diabetes or heart disease, then a simple healthy diet should be fine for you, including fruits and vegetables, healthy proteins including lean meats and fish, and avoidance of processed foods and excessive carbs.