Devolution (from The Fall) and "No New Information"

Well our chromosomes have two copies, which means mutations can be eliminated during mitosis as the chromosomes cross over, negating the effects of Muller's ratchet. Unlike bacteria for example, where only one copy of the genome exists. Of course if individual cells in our body do develop significant mutations, they usually experience a controlled death or are removed my the immune system.
And of course ageing is not simply a result of a build up of mutations. Other factors have a role, and probably more significant than mutations, such as the effects of immune cell responses or general wear and tear on the tissues, especially those that can actively regenerate, such as the nervous system. Even the oxygen we breath is damaging.