Install Adobe After Effects 7.0 on OS X Yosemite
You are going to need to download the latest version of Adobe After Effects.
https://www.adobe.com/products/aftereffects.html?promoid=KLXLW
I doubt are going to be able to download the old version of Adobe After Effects unless you go back to the OSX that used to be compatible with that version of After Effects (Which I don't recommend at all). You are just going to have to get used to the newer version of After Effects.