Surely, it feels really hard to go to the weight room but doing the weight exercise is really important after 50. Actually, weight training programs can reverse age effects.
Even if you are doing fewer repetitions, you must lift weights to keep your strength alive and your muscles strong. You can lift less weight with more repetitions.
Actually, if you are not doing the mobility exercise that will keep your muscles and joints working, then it will have a negative effect on your body.
You need to do Yoga, foam rolling, stretching, and massage in form of mobility exercises to keep your body's muscles and joints engaged.
Yes, focusing on one muscle at a time is right, but it is good if you are young. After 50, for your wellness, you need to do exercises that affect various muscles.
For example, you need to do the deadlifts and squats that affect the whole body and maintain strength and power in the body, keeping the body healthy.
Walking is great form of exercise after 50, as you don't get too much load stull it is healthy for you. But one thing you need to do is walk on hard surfaces too.
Walking on a plain surface can aggravate the risk of joint issues. So try walking on surfaces like rocky terrains, trails, etc., to keep your body running.
So this is going to ruin your baby after turning 50. If you are not doing any exercise, don't expect your body to give you help.
You need to at least do small activities like small runs, using stairs, stretching at home, doing yoga, etc., to keep your body moving & healthy.