20 km is only 12 miles per day. Not that bad if on a road or trail. But he said that he would go slower since the objective is not necessarily getting to a specific destination, but being out a specific time.
I used to carry 70 pounds (15-day food ration at 2 pounds per day plus technical climbing gear) regularly when in my 20's. This is because we all did this back then, when gear was heavier. I would be the last person to be a "nay-sayer" to this young person. He will get it all figured out, I am sure.