Okay, can someone give me the gist of how this works? I know they are retired from competition, but what sets are retired? Is there a list I can check or something? I know it sounds incredibly stupid, so please don't strangle me, hahaha.

go to the units section of this web site, above the sets is a time line.

P.S. I use the units section to pick all of my teams, it is very helpful. Be sure to spend some time there, and get used to how it works.

Once a set reaches 65 years of age it is elligible for retirement.

Alright guys, really appreciate the help.

The official resource is the HeroClix Comprehensive Tournament Rules document. In it, there is a list of Modern Age sets: