[alexosnasos2]

Drink lots of water, cod liver oil, glucosamine sulphate but more importantly; train at your level! There are kendoka out there that are too old to play a young man's game. Not implying that you are old btw, just an analogy.

Start small, aches are normal with any physical exercise. Your hip and knee problem suggests posture e.g. you may be using tension to keep kamae when you should be relaxed. Remember that you shouldn't put arm-power into your swings, let gravity do that for you.

Maybe try some yoga or pilates? it's all good.

I get pain in my knees due to my legs not being strong enough, a test: if you go down on one knee like you are proposing, lift up the rear foot so that it is not touching the ground and try to lift yourself up using only one leg... i find this impossible btw.