Male, 73, 5'5", 59.5 Kgs., Regular 5 Km. Morning Walk

Male, 73, 5'5", 59.5 Kgs., regular 5 Km. morning walk in 50 minutes, plenty of aerobic, stretching free style exercises. Have frequent pain in calf muscles, front of the legs, knees and cramps at feet and calf muscles, pain increases as the day wears off, obviously perhaps because of sitting for 7-8 hours at work, though frequently I get up and move/walk for 3-5 minutes. Remedy? Regards