Crazy that Bill was only 33 in this!
Born in September 1950, the movie came out in June 1984...making him even perhaps at the tail end of 32 when filming started!! He looked 45 to me easily. More people aged faster during the 80s and even 90s, but Dan Aykroyd looked way younger and more like a typical early/mid 30s dude to me. Egon could go either way I guess, lol.
As a kid I loved the scene where Venkman was shocking the college dude because he had a crush on and wanted to talk with the girl alone... but watching that now kinda creeps me out since he easily looks like he could be her dad.