Aging is the process of growing older. As you age, your body changes in different ways. You might notice the way you look on the outside, like wrinkles or gray hair, or feel changes on the inside, like needing more sleep. As you get older, your body may not work as well as it used to. That's because our cells (the tiny pieces that make up our bodies) don't work as well as they used to. Every day, cells in our bodies die off and get replaced, but as we age, our cells don't get replaced as quickly. This means it can be harder for us to stay healthy when we get older.