Aging is programmed: because the Hayflick Limit (number of times a cell is allowed to divide) is part of the bodies defences against cancer.

  Telomere shortening means that cells that replicate too much hit the replication limit, trigger p53, and self-destruct via apoptosis before acquiring enough mutations to become an cancerous tumour.

  Telomere shortening protects young organisms from early-onset cancers, but it causes tissue aging and degeneration later in life.

It's an evolutionary balance between cancer and health. https://wikipedia.org/wiki/Antagonistic_pleiotropy_hypothesi...