hate new photos- original iPhoto blocked in applications.

It seems that if you have an older mac you will be able to simply open the original iPhotos in the applications folder. However, my October 2014 macbook pro came with Yosemite loaded. I tried opening and received this message: "The version of iPhoto (9.6) installed on this Mac is not compatible with OS X Yosemite. Download the latest version for free from the Mac App Store."

Of course it came with this version and now it is no longer available from the store. Any suggestions as to how to revert back? Thank you.