You can use this tutorial on how to install AirDrop on Mac OS X Lion version in that case when you are running OS X Lion or higher version and don't see AirDrop in your Finder. If you want to change it please perform these easy steps.
These steps should be performed on any other Macs that you want to AirDrop with the older Mac.
Step 1: The first step that you need to do is to launch Terminal from your Applications: Utilities folder.
Step 2: Now please Enter the following text command into the Terminal window and then press Enter:
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 1
Step 3: After the second step is done, you need to enter this text command into Terminal to relaunch Finder:
Step 4: After you are done, you will be able to see AirDrop, that has appeared under the favorites in your Finder window.
You can easily reverse the text command by entering the following text command in Terminal:
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 0