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And with 5e there is no need to jump yo the full game after level 5.
The 5e basic game is my suggestion. That's what I am using with my kids (6, 9, and 14). Though with the release of PDFs of the 4e essentials stuff I am tempted to run that with them, but will probably stick with 5e for a while.
My initial advice would indeed be to check if there's an existing group somewhere he can join. If there is, best for him to start with the game that they play.
If there's no group he can join, or things are otherwise equal, I would say start with the 5e Starter Set. It's a good one. (The Pathfinder Beginner Box is also very good, but the jump from that to the 'real' game is much larger than with D&D.)
And with 5e there is no need to jump yo the full game after level 5.
The 5e basic game is my suggestion. That's what I am using with my kids (6, 9, and 14). Though with the release of PDFs of the 4e essentials stuff I am tempted to run that with them, but will probably stick with 5e for a while.