TIL Girls of the Kayan tribe start wearing neck rings at around 5 years old. The rings can stretch their necks to a length of about 15 inches (38 cm).

Ah, so THAT'S what they base vtuber neck lengths on!

It doesn't elongate the neck it actually shoves the shoulders and collarbone down. That's why they look a little like a wide based palm tree. The clavicle and scapula stay In place by the first rib but along the spine.