When I'm 64 starts off the last track on my album, A Beatles Collection. It is then followed in a medley with I'm Looking Through You. This lesson follows the way it was played, really with bit of improvisation, in that recording.
It is basically an alternating bass, almost ragtime arrangement that includes some tricky left hand stretches and fingerings. It would be reasonable to capo it to the second fret to make them a little easier.