Body is just like a burning flame. A flame exists and gives light so long as oil or wax burns. Fresh oil is drawn up into the flame and burnt out oil leaves the flame into the atmosphere. Similarly food, water and air enters into the body and used up and toxic materials leaves the body in the form of sweating, urine and stool. The body remains as burning flame giving beauty and youthfulness.
However the difference is that oil in the body is inexhaustible. It is the life-force(prana) pervading all parts and all cells in the body. The source of this life-force is the soul(atman) within each living being. Soul and its life-force is eternal, unending and uncontaminated. Hence so long as this life-force exists in the body, the body should be beautiful, youthful and uncontaminated with disease and death.
Again if we view the body scientifically, the cells in the body are being regenerated continuously. After every seven years all old cells are replaced by newly created cells. So after every seven years we get a new body and never remain the same. Hence the body should always remain beautiful and youthful.
So long as we don’t realise our life-force(prana) and source of this life-force i.e. soul(atman) or true self, we cannot remain youthful. In order to realise true self one has to practice Yoga. Yoga is a method to control body and mind and finally the mind. We are nothing but a mind. What our mind thinks up it materialises. When we practice Yoga to remain youthful and beautiful it really happens. We rule over the body and mind and overcome disease and death. This is liberation and this may come right in this birth.
Contrary to this, religious leaders would declare that disease and death is truth. So pray for the mercy of God and after death one may enter into heaven. Hell, heaven and God are imaginary things which have remained as ignorance and prejudice for thousands of years. They have no real existence; they exists in the mind only. These things have been created by a few in order to rule over the majority. The real truth, the real divinity and the real bliss lies in soul, life and consciousness only.