Will my knee joint wear out if I exercise a lot due to aging?

Hello doctor,

My question is regarding exercise. I am a 45-year-old healthy male who is 60 kg in weight. I was climbing up and down 18 stairs for exercise, but the family physician cautioned me that this exercise would gradually wear out of the knee joint as I am aged. Now I am doing stationary exercise, standing in one place I lift 2 kg dumbbells (a total of 4 kg). I lift the dumbbells above my head and then bring it down to touch my feet, so I nearly bend 160 to 170 degrees at the hip while trying to touch the feet holding the dumbbells. I sweat profusely with this exercise. I do it for 30 minutes regularly and use a timer for precision. Do you feel it is a good exercise in the long run? Will this exercise strengthen my vertebral column, or will there be any other problem in the long run. I have minor back discomfort in the lumbar area after doing dumbbells exercise for nearly a month. Will the pain subside as I continue to do the exercise? I love to do this exercise. Do you feel climbing 18 steps up and down for 30 minutes per day would be okay in the long run? I do not have to go out of the house doing this exercise, and I have found it helps me cooling my thinking process and better sleep. Please give your opinion on the long term effects of this exercise. Thank you.

Hi doctor,

Thanks for your reply.

I work in a sedentary job, managing a team in a healthcare BPO.