Some Lego is just for me, my nephew is good at building but these ones I build are pretty complicated, pretty large and a couple little errors at the start means they don't work. Not something I'll let him do. He'll get another one to do with me and him together, I'm thinking the Lego Technic Ducati Panagale and a Peugeot 9X8 24H Le Mans Hybrid Hypercar I have my eye on as well. We'll see. They all cost money and take time, I don't want to spend all my time with him building Lego. I'm an outdoorsman and want to impart that to him so we'll be out and about.
I find building Lego Technic to be relaxing. I get some snacks, coffee, some country music and I'm good to go for a few hours. I do other stuff of course, I'm sort of multi-faceted.
It's nice to have something so immersive that you lose yourself and have no concept of the passage of time. That can literally rejuvenate your soul. I took a look at the crawler crane and see now why your nephew will choose another kit for you to work on together. It is very advance.
I have no doubt that you'll be able to teach him as much about the outdoors as you will with the Lego. He may teach you something about mountain bike racing in return lol. It's a win-win!
My mountain bike racing days are over...I'm well into the mountain bike watching phase.