This may be lengthy, but please read on. My Wife and I booked this tour through Groupon, after completing the walk, at full price it is a bargain! Deacon John Larkin, was our guide, let me tell you, this man radiates passion for our country and founding fathers. He was born an raised in Boston, which is a nice bonus. As Americans, it is unfortunate, that we seem to forget or take for granted, our freedom and liberty. Deacon will re-infuse patriotism back into your blood. He is factual and describes at great length, the unimaginable sacrifices these 13 colonies made to secure liberty for their all who give their lives for it. The tour starts in Boston Commons at the Visitors Center, then ends at Faneuil Hall 1.5-2 hours later. Boston is fortunate to have this 'Son of Liberty' carrying the torch forward for our future generations. You will walk quite a bit, I am 48, an above the knee amputee, I had no difficulties. Remember The Beacon Hill area is not flat, but completely manageable.
P.S. - I hope your horse is returned by the Regulars, that will teach you not to lend anything to Paul Revere. :-)