When you become Identified more with the timeless inner body than with the outer body, when presence becomes your normal mode of consciousness and past and future no longer dominate your attention, you do not accumulate time anymore in your psyche and in the cells of your body. The accumulation of time as the psychological burden of past and future greatly impairs the cells capacity for self-renewal. So if you inhabit the the inner body, the outer body will grow old at a much slower rate, and even when it does, your timeless essence will shine through the outer form, and you will not give the appearance of an old person.
From Eckhart Tolle’s The Power of Now. Page 123