I don't know about any board games, but there is a really lovely online computer game called LOTRO that is really fantastic, if he's old enough for that (which I'd assume if he's reading those massive tomes). It's rated T (for 13+) but there are many younger players, and the game is entirely free to play now.
Many parents don't want their kids playing online games due to their (often deserved) reputation for bullying and harassment, but this game is actually quite different, in my experience. I've played loads of online games, and the population in this one is just different from the rest, possibly because it's a game dedicated to a fandom that is itself full of nerds and welcoming rather than snobby and exclusive, but it's probably more because players killing each other is not part of the main game, so that element of competition and enmity is not there. There are profanity and harassment rules in place that are enforced by vigilant moderators. The more experienced players with higher ranking characters tend to warmly welcome new players rather than chase them off, like they do in other games. I think it's ideal for a first online game or a younger player.
The game itself is "pretty old" - released in 2007 - but it's been regularly updated and has aged quite well imo, and it's still a great game. It's really fantastic and fun, and it's as true to the books as a game could get. The developers REALLY studied the source material, and it shows through beautifully. Crossing over the bridge and seeing Rivendell for the first time genuinely brought tears to my eyes, and finding all the places - the stone trolls from the Hobbit, the Brandywine, Tom Bombadil's cabin, the Shire - is exciting and simply wonderful for a nerdy fan like me! It's just a gorgeous, accurate way to immerse oneself into Middle Earth.
The game being older means that the servers aren't exactly overflowing with players, but it's a rich and fascinating world with enough content for a single player to enjoy on their own for probably a year, maybe more. I really can't recommend it enough.