Why is Mitochondria different in the cells of older people?

Well, mitochondria are the energy supplying organelles.

Knowing this, the mitochondria is different in the cells of older people because its been damaged, its called Mitochondrial Aging. When mitochondria age, just like us, they get damaged. And when they get damaged they damage our age, in a sense that we get older. This is how it is different in older people.