ipad cannot print natively to anything except an airprint printer.. that is a different protocol and the printer must be rated as airprint capable and it must be network connected by wireless.. Not plugged into the USB of the AE.
See the info from apple about airprint.
http://support.apple.com/kb/ht4356
There are apps available for ipad to help you print to a standard printer.
And there are apps you can install on a Mac.. to allow it to be airprint server to the network.. sort of.
See Printopia. http://www.ecamm.com/mac/printopia/
There is a free trial.
For ipad.. there are a number of apps.. I do not use it so I cannot tell you what is good or not.
https://itunes.apple.com/us/app/printer-pro-print-documents/id393313223?mt=8
https://itunes.apple.com/us/app/printcentral/id366020849?mt=8
You can just google for print apps for ipad.