A bunch of examples about which we weren't sure in TLP:
Alouette: Zig-zagged. While some jurisdictions may have laws on the books punishing under-18/over-18 relationships even with minimal age gaps as felony sexual offenders, many others don't, especially when it's done as part of marriage with parental permission.
Banished: Citizens become adults at the age of 10.
The Sloosha’s Crossin’ an' Ev’rythin’ After section of Cloud Atlas is set in a future After the End society in Hawai'i implied to be descended from Americans. In this culture, children go through a Rite of Passage at age 13 involving spiritual communion with books and the spirits of the ancestors. This society has a pretty limited amount of law and lacks things like age of consent, but after Zachry goes through the ceremony, he's pretty much treated like an adult.
Galactic Milieu: The age of majority in the Milieu is sixteen.
The Hunger Games: Kids are reaped for the Games until they are eighteen, so no one makes adult life plans until after their final Reaping Day has passed.
In Savvy and its sequels, people with the right gene get their savvies (essentially superpowers) on their thirteenth birthdays.
Sonic The Hedgehog Satam: In the episode "Drood Henge," the Freedom Fighters are attempting to get information on Robotnik's latest a scheme to acquire the fabled Deep Power Stones from Nicole. Unfortunately King Acorn has placed a time lock on the data, preventing Nicole from saying anything until Sally comes of age at 18 (two years from that point). Fortunately Sonic is able to persuade Nicole to break the lock early by pointing out that the most likely result of Robotnik retrieving the Deep Power Stones first is the final conquest of the planet, thus making it illogical to withhold the information any longer.
In Star Trek, a species called the Klingons has their "Age of Ascension" somewhere in their adolescence, and it's when they become warriors.
Tales of the Branion Realm: The 16-year old Crown Prince is above the age of majority and thus old enough to lead a siege.
The True Love Loophole: Wonderland has a younger Age of Majority due to its history of war.
In Warrior Cats, cats are considered adults once they have reached the rank of warrior. On average, this tends to be around 12 moons of age, but it does vary by individual.
An older age example - in Wynonna Earp the eldest child of each Earp generation gets to be the "chosen one" on their 27th birthday.
In Young Dracula vampire children appear to be normal humans (give or take a few magic powers), but on their 16th birthday have to face their evil reflections in a magic mirror to become full vampires.
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman
A bunch of examples about which we weren't sure in TLP:
"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman