So at 40, Egon is too old to go Ghostbusting with the team?
Now I haven't watched much of this series(I was a Ghostbusters fanatic as a kid and watched the movies and the Real Ghostbusters), but I read that Egon is 39 going on 40 and that the original Ghostbusters are retired due to age, with Egon acting as sort of the Zordon or Master Splinter who is the obvious leader and mentor but stays at their headquarters and doesn't usually get physically involved. In the movies, Egon was most likely 40 when he and the others started the Ghostbusters, as Harold Ramis was 40 when the movie was released.
I guess it just seems a bit silly and ageist to me that everyone in action-oriented kids shows has to be either in their teens or twenties to do heroic stuff and retire by their 30s. It's especially silly when you consider the Ghostbusters were all past their 20s in the movies and yet they were all de-aged for the cartoons.