I'm 71, and after a lot of backpacking had to give it up (weak disk, muscles not as strong, not as much endurance).  But last year my sons took me on a Q trip for a week. And now, inspired by a trip report thread going on at the same time (Thread started by Solus, "October 2010 solo" or something close to that title) I'm thinking of a fall solo this year, if I can hold onto some vacation time from work (paddling some western canyons also beckons).  Anyhow, I can state definitively, you are not yet a senior paddler.  No law against a youngster like you using some wisdom about where you place that foot of yours on a portage and how much you carry.  Congrats on your recovery; you and the others here inspire me.