To stop or not to stop?

When should one really stop working and why does one continue to work? I think the answer is as long as one can work and more importantly is wanted one should continue to do what makes him feel comfortable.Of course there are many reasons to work ,one of which is financial.Its good to be financially independent and to be able to feel that you are still able to contribute one way or other.Its a nice feeling waking up every day knowing that you have a schedule ahead for the day as compared with waking up and not knowing what to do.
But sometimes your body sends you signals.....you become forgetful and the body feels tired and work which you enjoyed doing before becomes chores.Do you ignore such signals or balance them against the reasons for working?Someone said "you should not overstay" but looking at some of the senior people still in office one tends to be inspired.I have always subscribed to the belief that if others can do it so can I.It would be nice sitting at home not really doing anything but then what? Someone said some are destined to die on the job and maybe I could be one of them because at the end of the day I cant imagine a life of senility and sitting waiting to be called!