At the level he's playing at and the age he's at, just make sure he enjoys himself. I played a lot of golf between 10 and 14 but felt forced and stopped enjoying it so simply turned to other sports. It wasnt till I moved to university and started playing out of sheer enjoyment that my handicap came down.

For the first two years I was playing 5 rounds a week in bounce matches with mates then and 2 evenings at the range with 1hr on range and 1hr chipping and putting (I only had 2 days where I had lectures!) Then I joined a club and got a handicap of 12. 2 years later I've left with a handicap of 4.
Id recommend that when you play rounds with him, try to make sure your playing with good golfers- the best way to learn is by watching them plot their way round the course and trying to match them- Both my flatmates were scratch golfers and I got fed up losing to them! You'll find he'll soon start to catch up