[bhaak]

These are advanced subjects and even a proficient programmer doesn't need those very often.

The advantages of Ruby as a first language IMO are that it is a pure OO language. No special cases, no unnecessary boilerplate. Much better than Java in that regard. But you could argue if nowadays you still need to focus that much on OO.

I'll be interested on the book turns out. Usually, I wouldn't recommend a generic programming language as a a first language for kids. I would use something with turtle graphics and a REPL.