https://www.metv.com/stories/the-creators-of-leave-it-to-beaver-creators-were-worried-viewers-wouldnt-like-the-series-once-the-beaver-grew-up

Would The Beaver be as funny if he wasn't a kid?

Older Beaver wasn't as funny.

One thing the show runners did in later seasons was to do more scripts with the Wally group, especially recognizing the asset the Eddie Haskell character was.