The problem here is you’re talking about to different things. Exercise causes cells do die, but because it damaged the cell. Aging happens because of changes to the DNA, not the cell itself. Basically with time, DNA changes and gets bad at replicating (telomeres shortening), so cells don’t replicate and create new cells as they used to. When exercising, you damaged cells, but it doesn’t affect your DNA, so it has no effect on aging. You’re fine!