How do I transfer my Itunes music from my MacBook to my IPad Air?

You don't need a USB port on your iPad, you use the charging cable to connect it to a USB port on your Mac.

If your Mac has a OS X 10.6.8+ on it, and you have the current version of iTunes installed on it, then you should be able to sync your music from your Mac's iTunes library to it : connect the iPad to yoru Mac, select it on the left-hand sidebar of your Mac's iTunes (option-command-S will get the sidebar to show), and then use the Music tab on the right-hand side of the iTunes screen to select the music that you want on your iPad.

Syncing media : http://support.apple.com/kb/HT1351

You may also find this page for syncing to a new computer useful : https://discussions.apple.com/docs/DOC-3141

Use the lightning to USB cable that came with the iPad. Start iTunes 11.1 or later on your MacBook Pro and connect your iPad using the cable I mention.

I believe the key issue here is making sure to be using the latest iTunes version, currently 11.1.4. Earlier versions may not know how to "talk" to the latest release of the iPad, especially if they date back from 3 years ago.

You can download the latest iTunes from http://www.apple.com/itunes/download/ then double-click the .dmg to open and double-click on the installer. It will install on top of the previous version with no loss of content. Given that you state the Mac is 3 years old, it should have at least Snow Leopard, if not Lion, so you should be fine from the OS perspective.

And like the King stated above, your Lightning charging cable that came with the iPad IS USB!