My son turned 5 in October and has played the absolute shit out of BotW (beginning when he was 4)—it is far and away his most played game and it dwarfs the time he has spent with all other games combined. Also, I did not push him to play the game—he found it all on his own—and I rarely help him as he plays.
I think people here both underestimate kids, and also misunderstand what they want out of a game. He doesn’t care whether he beats the game or really even if he progresses at all. He just loves doing his own thing and BotW is the absolute perfect game for that.
To put things into perspective, he dabbled in Minecraft but never really got into it, and stuff like Kirby or Yoshi (all of which are available to him) have never hooked him. Despite what you might guess, a game like Yoshi’s Crafted World, while easy, wasn’t really all that interesting to him. Again, he wasn’t in it to beat the game so the fact that it was easy didn’t really work in its favor. He was pretty bored by it because it was still too hard for him, and being hard meant that he couldn’t really play it as the difficulty prevented him from doing anything within the game world.
BotW, on the other hand, provides him with a nearly unlimited playground full of opportunities to explore. It doesn’t matter if it is hard because there is always something to do that is accessible to him. The more he gets into it, the more he enjoys it and I am constantly surprised at the things he comes up with.
Also, he plays it without being able to read anything. A five year old doesn’t care about the story or even doing things according to the game’s plan. Text is irrelevant.