Sorry, but there are no golf courses in Mahdia itself although if your dad is desperate Nour Palace Hotel and Mahdia Palace Hotel both have pitch and put type greens!
Monastir is an hour away by train, but have no idea if the golf course is near the station.
If he would like golf to be a major part of his holiday, could he perhaps change his hotel to one in either Port el Kantaoui or Hammamet. Both resorts are geared up to welcome golfers in a big way. Hope that that is some help. Jenny