The idea of 13 was fine at the time, but it struck me even to wonder if the First Doctor was the First... after all, 'tis a bit hard to swallow that he would manage umpteen hundred years with nary a scratch of his shiny regenerations, then in the pace of what 20 years? use up 5-6 as if they were tissues.

And it's even worse now, not even half a century and he's used ten... maybe he should consider finding a nice safe hideaway for a few centuries once he hits 12 :)