My Dad was 80 on his last Quetico trip with me and my Brother - like you stl, we wanted to do another trip with Dad.  I don't remember the particulars, but it would have been something like 120 miles and 50 or more portages.  I still consider that to have been one of the toughest trips I have ever done, mostly due to conditions.  We didn't let my dad carry the 69# Grumman, but he did carry a pack each trip across the portages - we double trip.

In hindsight, I wish I'd started getting lighter gear back then, rather than a few years later.  Now, I've gone to ultra-light gear for everything, planning on continuing my trips to Quetico as long as I can - making the trips a lot easier, even now,  by carrying less weight.  If I'm not in the Q at 80 (I'm 58 now) it'll be because my knees give out, but I'm planning on being there.  Looking forward to retireing someday, so I can spend more time, maybe longer trips, and trying some other loacations.