Different Node versions in OS X El Capitan Is it possible to run different Node versions in OS X El Capitan with Homebrew?
Yes. When node updates a package, it doesn't remove the old version. You can also install old versions of a package using brew versions, but you will probably need to install the boneyard tap in order to be able to do this. See here and here.

Based on this answer:
Use ls $(brew --cellar) to determine what you have installed, and brew ls -v to see installed packages and versions. You can then call the installed binaries directly (or make your own aliases to them).