The dumbbells that you should lift while exercising depends on your body weight height and your body mass. The weight of dumbbells that you will carry also depends on your strength and your age. The purpose of weight lifting also affects your weightlifting routine. Are you lifting weight to gain body mass? Build muscles? Just to stay strong and healthy? Or to tone up your body? The heavier dumbbells you carry the more strength you need and the more your muscles grow.
If your body weight is between 60 to 75, you should start with a set of dumbbells weighing 25-35 kg, do two sets of 10 each side every day for a week or up till you get used to it and then increase the weight gradually along with the number of sets. You can also start with lighter weights and graduate to heavier ones. I suggest that you take a trainer's help to make a training and weightlifting schedule for you.
If your body weight is between 60 to 75, you should start with a set of dumbbells weighing 25-35 kg, do two sets of 10 each side every day for a week or up till you get used to it and then increase the weight gradually along with the number of sets. You can also start with lighter weights and graduate to heavier ones. I suggest that you take a trainer's help to make a training and weightlifting schedule for you.