That’s a good thought! DNA and RNA have many regulatory elements though which can cause proteins to be made or to stop them from being made. It could be that a regulatory element on the ends of the telomeres stop these toxic proteins from being made, but when we age and the telomeres shorten the regulatory elements get lost. This causes the toxic proteins to be made, causing age related damage.

ELI5: The off switch for the toxic proteins could be on the ends of the telomeres, and when they shorten the switch gets turned on, causing age related damage.