The wear and tear theory of aging is just one of many currently popular, the body is not a mechanical machine necessarily bound to wear and tear, it can in some cases successfully heal itself, some species basically don't age (some can actually revert in lifecycles).

A competing theory is programmed aging (in which "clutter" would be an effect of, not a cause): http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1369273/