There is a problem with installing Git on OS X: it is already installed on the system and just does not update it. Each time you upgrade the OS, install it again.
For example, at the time of this writing, the current version of Git is 2.5.1. And in OS X Yosemite is sewn up 2.3.2.
When installing a new version through Homebrew, it still remains inaccessible.