Did you know our bodies can be younger or older than we are? Maybe you are ten, but your body is twelve!

你可知道，我們身體的年齡可能會比實際年齡年輕或者年老呢?

Our bodies' age shows how worn out our cells are. How do scientists know they are wearing out?

身體年齡從細胞衰退的程度可以看出來。那麼科學家怎麼知道細胞正在衰退呢？

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