How to Enable AirDrop on Older Macs

If you are a Mac user you probably heard about AirDrop feature, it provides a quick way to share files wirelessly between two Macs, without having to connect to an existing network. However, if you have an unsupported Mac, you can still use AirDrop by following these instructions..

AirDrop is available from the Finder, the Share menu, and in Open and Save windows. When you choose AirDrop, OS X looks for any nearby computers that have also selected AirDrop.
STEP 1: Launch ‘Terminal’ app from your Applications:Utilities folder.
STEP 2: Enter the following command into the terminal window:
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 1

STEP 3: Then enter this command into Terminal to relaunch Finder: killall Finder

STEP 4: Once you done that, you should notice AirDrop appear under the favourites in your finder tab.

NOTE: You will also need to perform these steps on any other Macs that you want to AirDrop with the older Mac. You can easily reverse the command by entering the following command in Terminal:
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 0

Source : iclarified