I would rather recommend to start with traditional medium first. It’s right that today you have to use digital tools to get the work done, but you still have to master the fundamentals in order to use those tools properly.
The first thing to do, I think, regardless to the medium you’re using, is to learn anatomy and perspective. There are tons of books out there to do so:
Then you can read these books by Scott Mc Cloud, which are indeed great to learn how comic book storytelling really works.
But as far as art and drawing are concerned, he has to try and find what tools fit him the most, and it’s a long process. So your suggestion of just starting with pen and paper was a pretty decent one in fact. You can add a lighting table, rules and compass, indian ink and a variety of brushes and pen, white ink , copic markers for black and white work as a start. For color work digital can be great but it would also be good to start with traditionnal paint as acrylic or watercolor. Here’s a website where you can find pretty all what’s needed to do comic books art:
And here’s another one exhaustively listing what’s needed at every step:
Anyway, what’s really most needed is practice, practice and practice again! Drawing is like music, you have to practice the grammar every single day in order to create very personnal and original stuff!
Anyway if it trully is your nephew’s passion, he will never stop practicing and will eventually find what he needs to get the job done.
Hoping that helps.
I wish him (and you) my best.