My late Dad always told me too work SMARTER not HARDER ;)
The older I got, the more I realized what that meant.
A strong mental attitude will do wonders especially as the body ages.
I need my 8 hrs sleep, always have even when a young guy.
I'm a side to side sleeper, but if I wasn't, I'm be in a hammock for sure.
I once saw a couple on Quetico lake that were easily in their late 70's-early 80's. He was humping the canoe and a food pack, she had a big Duluth pack. The said they had been tripping since they were in their teens.
They only went for shorter trips now, 4-5 days and back. Sometimes a long hard portage WAS the days trip ;) There's NO reason your Dad can't go until HE decides his body can't take the rigors. Let him set the pace and decide what he wants to carry. He might end up outworking you ;)