I fly a PA28 and I'm 6ft 2. I've not had a problem, but if he sits in the front (which he'll probably have to) expect a lot of rubbing shoulders, especially when trimming, and makes sure he keeps his feet clear of rudder/brakes.
As above poster said though, seating five, is beyond the certification of a PA28. It was designed as a family tourer, 2 adults and 2 children.