2007 iMac

Before leaving for summer break, my university held a technology sale offering both their Dell and Mac computers. The Mac computers being sold were from 2007 with one 2009 model. I purchased a 2007 iMac for only $100. I was able to test it after purchasing it, and it worked well. Other than the outdated OS X 10.11 El Capitan from 2015, everything was working fine with the computer. It’s 27" screen was a major selling point for me since it’s easier for me to see. I can’t read computer screens very well. I was wondering if the iMac would be useful for me in college. I believe the hardware and software are fine, but my major concern would be Apple’s discontinuation of updates for its operating system. Could it pose a significant enough security risk to render the desktop useless? I looked at Apple’s website for their newer computers, but they are too expensive and the Office for Vocational Rehabilitation can’t purchase one since they don’r consider computers, or even laptops, assistive technology.