I want to study Ruby and RoR for some things I’ll have to make, but almost every book, videos or any kind of source I find is outated, where the most current book I could find (link here) is one of the version 2.1 (latest stable version of Ruby is 2.2.0), and in the case of Rails I only find books about RoR 3.x or at most 4.0 (latest stable version is 4.2.0).
Then I wondered if there are many changes in Ruby and RoR, for example, if I find a good book about Ruby 1.9, should I read it?, are there many changes?, the same in the case of Rails, if I find videos of Rails 3.x, should I see them?.
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I would say that it is never ‘obsolete’ to study outdated software.
For sure, there are changes, but what you learn in the earlier versions will translate pretty well, in newer versions.
When you hit things that are different from an earlier version of the language or framework, then you have the current documentation (and version) to explore those changes that you are using.
A lot of the ideas in the books relate to later versions, though some features and syntax change.
This is pretty normal.
The current language version that you learn today, will undoubtedly help you for tomorrows current language version.