Hi mr Ashok, As you described your complain there are two different problems. Both are commonly age related problems. 1.back ache radiating to left lower extremity.this could be due to lumbar spondylosis.which is age related degenerative process causing compression of nerve root on left side. If it s a recent onset problem than you cocktail of analgesics, antacids,Pregabalin, methylcobalamine and good anti inflammatory medications for pain relief.BUT the main stay of treatment would be lifestyle modification ,wt loss some back care and exercise of back once pain subsides. if after a month pain persist or increases Than go for spine surgeons opinion. 2.knee pain on standing up also seems age related osteoarthritis. in that too.life style modification like avoid sitting crossed leg, squatting or sitting below the level of knee height,prolonged standing,prolonged walking(can walk for long distance but after short duration of walk take more rest by sitting in between) will help slowing down the degenerative process.sos analgesics can be taken on rise in pain. And last but not the least accept you are getting old. know your limits. avoid extreme physical activities. Visit orthopecian and follow the advice. :)