Hey, I don't know it things will be adjusted before a majority of people check this, but if you're on Minecraft and you can't connect to the server cause it is running an old version, Mojan put out an update to 1.6.4, now panic for a second until the next paragraph starts.
Okay stop now. So luckily we have a new Launcher that let's you revert back to previous installed versions, in case you have never done this, here are instructions on how to de-grade(cause opposite of upgrade):
Now rejoice, but be wary, if you want to play the next update that comes out, you'll need to go back and tell it to use latest.