In young people, when a cell goes bad it is destroyed and replaced by a nearby good cell by it dividing. An older organism, which has shorter telomeres, has to hold onto bum cells. This could be why there is a correlation between shorter telomeres and bum cells. One does not directly cause the other. Cells routinely become dysfunctional and when cell dividing is inhibited the bum cells accumulate. I know that "group selection" is controversial but imagine, a billion years ago, many groups of bacteria that hadn't come up with telomeres yet. Each group is having lots of deaths due to limited food. One group develops a way to kill off the older cells disproportionately. The cells in this pond will evolve more quickly because they have more generations per year. Being more evolutionarily advanced they take over and ever since we have been having organisms die of old age. It may be that telomere shortening evolved to stifle cancer, or to kill off the older generation, or both. It may be possible that increasing an older organism's telomere length may actually reduce cancer risk. If you do this then cells can divide and the organism will start to destroy bum cells and replace them. Bum cells that may have been close to becoming cancerous would be destroyed.