iPad Air 2 ships with iOS 8.1, so development requires Xcode 6.1, not 6.0.
Xcode 6.1 also supports OS X Yosemite, but it can also start with 10.9 (Mavericks) - you do not need to update your OS, just your Xcode. (Upgrading to 10.10 is a good idea at all.)
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