There is no doubt aerobic exercise is important for overall health. We don't want to diminish its significance. However, if you want to get into the best shape of your life, weightlifting is more important than cardio. As we age, it is often not our aerobic health that causes us to become debilitated. It is the loss of muscle mass and bone density that causes issues as we get older. Only weightlifting will build muscle and increase bone density.