This is a great question! There was a debate for a long time about whether older adults use their brains more or less than younger people. We know that older people have smaller brains than younger people, because the brain cells die off and aren’t always replaced over the lifespan. Right now, we think the healthiest older adults use more of their brains to make up for fewer overall brain cells. Older adults who aren’t as healthy can’t use more brain power to make up for this loss.
But there is a lot of new science coming out about this every day. My answer might change in just a couple of months!