IOS development on Mac mini mid 2011
In general, if your Mac runs the current OS - you can run all the Dev tools needed. In specific, that Mac meets all requirements for OS X 10.11 and Xcode 7
Xcode 7.3 system requirements
You want to start your machine to support Xcode 7.3 (which is now still in beta, 25 feb 2016). Xcode 7.3 beta requires a Mac running OS X 10.11 or later.
These Mac models are compatible with OS X 10.11, aka 'El Capitan':

MacBook (Early 2015)
MacBook (Late 2008 Aluminum, or Early 2009 or newer)
MacBook Pro (Mid/Late 2007 or newer)
MacBook Air (Late 2008 or newer)
Mac mini (Early 2009 or newer)
iMac (Mid 2007 or newer)
Mac Pro (Early 2008 or newer)
Xserve (Early 2009)

So, you should be good to go and start developing!
Source:

https://en.wikipedia.org/wiki/Xcode#7.x_series
http://adcdownload.apple.com/Developer_Tools/Xcode_7.3_beta_4/Xcode_7.3_beta_4_Release_Notes.pdf
https://support.apple.com/kb/SP728?locale=en_US