I have aching and pain in my left leg when I walk and my left buttock. When I stop the pain goes. I am 67 years old?

Radiculitis. Your spine may be the culprit! A Disc problem at level Lumbar vertebra # 5 Sacral 5 can be the reason for the pain in the distribution you describe. See your Primary Care Physician for an exam and perhaps a Lumbar MRI Treatment is available!