Hi doctor, i have serious ache and pain in my right leg and thigh, when i walk for long a feel aches and pain in the same leg.

Many possibilities: The most likely cause at your age is a muscular strain but other possibilities that are less likely are hip, knee or spine arthritis, and even less likely is circulatory disorder. You need to be examined. X-rays may be needed.

Multiple causes: One to consider in someone who is about 70 years or older (sometimes as early as in the 50s if a heavy smoker) is peripheral arterial disease, a component of which is intermittent claudication. This is a pain in the thighs and/or calves which occur with walking almost always the same distance. It resolves with rest and occurs because of blocked arteries. See a vascular surgeon if you're concerned.