The unasked question

There has been a lot of comment and commentary about the decision of Arlen Specter to switch parties. The one question I have not seen raised is why does a 79-year old man think he should continue being a senator. Doesn't the time come for the old to step aside and make way for the new? No eighty-year old is as mentally sharp as they were when they were 6o. Can anyone take a senator like the senior senator from West Virginia seriously?