While "Mature Thumbs" is not a single known product or brand, the phrase is frequently used by reviewers to describe something that has evolved into a more sophisticated or well-rounded version of itself.
The "mature thumb" average length (roughly 2.74 inches for men and 2.49 for women) is a critical benchmark for smartphone manufacturers designing screens that can be navigated with one hand. Community Perspectives “Guys in there are both young and mature. Thumbs up!” Travel Gay
When applied to books, a "mature" rating often refers to the depth of themes or the skill of the creator relative to their age.
Reviewers often give a "thumbs up" to designs that trade "busy" looks for clean lines and better proportions. Literature & Creative Works