My Gf’s kid just started playing BotW about a month or two ago. He beat it last week and is now just Lionel hunting for sick gear. I haven’t played a lot and he’s way better at it than me. So I don’t know. His birthday is coming up in 3 weeks. Should I get him TotK?

Looks like he both liked it much and is very good at it, so I don't see why not.

Yes before he becomes a EA sports or COD fan and loose all sense of great games.

Yeah, absolutely.

My kids grew up with Zelda, younger one always loved it and OoT is his favourite, but he didn't like BotW much, and didn't even want to try TotK. Older one always liked Zelda games, but never quite had the patience to solve the Temples (he is on the spectrum, lighter case. but nonetheless), so BotW really spoke to him with lot of roaming around and short shrines (and yes, Lynel hunting), and was equally enamored with TotK.

He loved Elden Ring as well, but I'm not sure if there's any correlation between that and BotW/TotK, given that he loves Dark Souls and is really good at it.

If it's a month after beating BotW it sounds like excellent timing. Go for it.
I imagine a kid could have a blast with the fuse/ultrahand mechanics. Or the young at heart like myself :D

I thought it would be too soon. I myself am not used to getting a new Zelda right after finishing one. Usually it comes many years later. But that’s reassuring. I’ll talk to his mom and we’ll get it for him. I did hear tofk raises the scale of what one considers great.

Depends. There are plenty of folks, even around here, who think that TotK, for all its additional stuff, is still not as good as BotW, or at least not as fresh.

Depends on the kids interest levels. I say you should get the game for him, but I also say that if he’s happy with the game as it is right now, I’d suggest letting him stay focused on BotW for a little longer. No need to rush him along to the sequel. One month is not nearly enough time to get everything out of that which BotW offers.

My twins are 12 and loved breath. They loved tears even more. Go for it would be my view.