Other than your Switch being in danger of dropping to the floor I see no reason why 5 y.o. shouldn't play Zelda. He won't beat it, but he will try to figure it out at his own pace and will have fun with it in his own way. I think when we were kids beating game weren't that important.
It might be too advanced because of the level of hand-eye coordination required to be successful.
That being said, it doesn't hurt to let them try and watch them explore. Your kid may have a knack for it.
With my daughter, 4yo, we tried together and she likes to wander the open world and help me cook but shies away at combat.
I introduced her to Kirby via the Virtual Console and she's really taken to that. Because of this, my strategy has been to have her experience different generations of games in succession until I can see she's comfortable managing more modern games.
A couple of exceptions to this have been Sayonara Wild Hearts and Mario Kart 8. Very easy to pick up and play with tons of assists to help novices get acclimated.
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.
My daughter is young and she absolutely loves catching the horses and riding them around. I had to get her off the plateau but after that it was a great game for her. She also likes changing Links clothes, chasing the foxes and other animals, etc, etc. It's great for little kids. Of course she's never going to get anywhere or beat the game, but that's not really the point of gaming for kids.
People have to remember little kids don't play games to understand their mechanics and beat them, they just pick up the controller and run around in circles having fun. I'd turn on god mode in Oblivion (pc) for my son when he was little and just let him wander, he'd end up collecting sweets around town and organizing them on a table for an hour... he never really killed anything or cared about the story, he just wanted to collect all the donuts in the world.