Is Apple slowing down older iPads too?
According to Apples Information the iPads should not be affected.

Apple Support Document:


  With a low battery state of charge, a higher chemical age, or colder
  temperatures, users are more likely to experience unexpected
  shutdowns. In extreme cases, shutdowns can occur more frequently,
  thereby rendering the device unreliable or unusable. iOS 10.2.1
  (Released January 2017) includes updates for previous models of iPhone
  to prevent them from unexpectedly shutting down. This includes a
  feature for iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, and
  iPhone SE to dynamically manage the instantaneous performance peaks,
  only when needed, to prevent the device from unexpectedly shutting
  down. This capability was also extended to iPhone 7 and iPhone 7 Plus
  with iOS 11.2, and we will continue improving our power management
  feature in the future. This feature's only intent is to prevent
  unexpected shutdowns so that the iPhone can still be used.


So the feature (or issue as some see it) is not present on the iPad.
The iPad under the circumstances that the battery can't deliver the necessary power would shut down and not try to throttle performance.