OK, I am bad with metric. But those distances do not seem like that long- not what I would call a thru-hike, more of a long hike. He has been outdoors (not really a newbie then), long canoe trips (OK with being away from civilization). I would think the issue would be the pack on the back (I do not see how a weekend trip would match that) and walking (think feet). I think a good plan would be do do the trip, but start with low daily miles and work up to what he can do.

I have had real newbies (for example a 16-year old from New York City who had never walked off a sidewalk or seen stars) on a 35-day NOLS course and most did just fine - only a few did poorly. One thing I noticed is that young folks did better not that they were in better shape, but they had an open mind for new experiences. So if your guy has an open mind, that is really good.

So, I say go for it! And if it goes bad- well that is a good test of your relationship too. Sometimes the harder it gets the gooder it gets between people.