Leave It to Beaver S06E15 - The Mustache

After finding out that his steady girlfriend started going out with a new boy at their high school that has a mustache, Wally takes Eddie and Lumpy's advice to grow a mustache, thinking it will make him more mature. However after doing so, Wally soon discovers that his newly grown mustache doesn't have the affect on Julie's opinion of him as he originally thought it would.