Drewfus,

Mk631 has provided a good summary of the pros & cons of the various northern entry points.  

Also, ditto on what both he & Dd had to say re: age.  On the other hand, if you don't care care of yourself, the aging process certainly compounds other issues you may have.  The older you get, the harder you need to work at it to stay in shape due to muscle & bone atrophy as well as changing metabolism issues.  Mainly, you just need regular vigorous exercise if your doctor allows it.  The reason I workout nearly 2 hours daily EVERY day is to stay in reasonable shape for Canoe Country (& because health care as a retiree ain't cheap; I want to minimize my need after retirement).  Knock on wood but, at age 55, I haven't backed off much on my tripping practices from 20+ years ago.

Also, I would elaborate on Mk631's info re: Beaverhouse.  Technically, of course, BH is NOT an entry point.  However, when you LEAVE BH, you can reach 3-4 different entry points.  They include: Quetico, Cirrus, Three Mile (just east of it, really), & LLC.  Frankly, BH is NOT the best way to reach either Three Mile or LLC.

The put-in portage to BH is mostly flat, sometimes featuring a mud hole or two & about a 1/4 mile in length.  If you head to Cirrus, you have a very flat 1/2 carry to No Name, then a somewhat short but twisty-turny portate with ankle-buster rocks to take you into Cirrus.  From there, you're golden; LOTS of water to cover with absolutely NO portaging.

The Quetico portage climbs a small hill parallel to the rapids but it's no big deal & very short.

Make sure your dad is getting in some regular exercise a minimum of six weeks prior to your trip.  Then follow Mk631's advice on routing & you should be fine.

Jimbo   8-)