According to Chinese medicine The Kidney energy gives us the foundation for life. It is the source of our Yin and Yang of the body, and keeps up the ancestral energy our parents gave us. During our life we are as strong as the quality of the kidney energy we got from our parents plus what we eat and the fresh air we breathe (that is the energy we create on day-to day basis). If you did not get strong kidneys (we also call it weak constitution) you age faster and become weak faster.
However, even with strong kidneys when a person is getting older, he/she starts getting problems with low back pain, and knee pain (this is a sign of Kidney Yin energy not so strong). Frequent bladder infection, a swelling of ankles, being cold especially when you go to bed are signs of Kidney Yang failing). If we experience any of these symptoms, we need to start paying more attention to our Kidney energy. However, we also need to start paying more attention to the quality of food we eat in order to supplement our ancestral energy with the daily post-ancestral energy coming mostly from food and air.