The phrase does not appear to be a widely recognized idiom, meme, or specific cultural reference. Given the unusual nature of the phrasing, it likely refers to one of a few niche contexts.
: A list of 40 specific tips for maintaining "mature" (established) perennial gardens. 2. Digital Literacy and the "Mature" Demographic 40 mature thumbs
In the tech world, "thumbs" often refer to how we interact with mobile devices. A post titled might explore: The phrase does not appear to be a
: A fictional tale about a mystical artifact or a peculiar collection (like a wall of 40 ancient stone thumb sculptures). 40 mature thumbs