Whatever age you are, your body is much younger. Most of the body’s tissues and cells are constantly regenerating themselves.
According to a method of estimating the age of human cells by Jonas Frisen (not one of the Jonas brothers, apparently), the average lifespan of all the cells in a human body is 7 to 10 years.
Your red blood cells last only 120 days and your liver is entirely replaced within 300 to 500 days (shorter if you’re Irish, probably).
And the entire human skeleton is thought to be replaced every 10 years or so.