Can i use my iMac (21"5 Late 2012) as a monitor for my Playstation 4?
Can i use my iMac (21"5 Late 2012) as a monitor for my Playstation 4?
iMac (21.5-inch, Late 2012), OS X Yosemite (10.10.4)
Sorry to tell you what you don't want to hear but unfortunately no. Please don't ask if I am sure or if there is any way, there is not.
Please read Apple's Use your iMac as a display with Target Display Mode - Apple Support. In it you will see the only way to use your 21.5" iMac as an external display to another device is to use it with another Thunderbolt equipped Mac, for example a MacBook Air, Mac Pro, iMac, etc...