Juvenile Delinquents are underage and younger villains who are under the age of 18 in a biological age, or in simple terms: young criminals; due to this they are rather difficult to deal with as they are normally too underage to be dealt with as adults. They can be aged as babies, toddlers, teenagers, and preteens.

Adult villains who started their villainous acts since their youth or their earlier childhood life can be added here as well (e.g. Lord Voldemort, Bill Cipher, Dr. Douglas Grey, Light Yagami and Scarlet Overkill). Characters who can't apply to this category are those who possess the body of a child or teenager for their nefarious plans (e.g. The Core, Emperor Belos, Dr. Eggman, and Truckenstein).

Examples includes: Andrew Detmer, Three, Four and Five, Eric Cartman, Darla Dimple, Carrie White, Cid, Sid Phillips and Princess Morbucks.

They are the opposite age of their older counterparts that are Elderly and the villainous versions of their heroic younger counterparts.

Note: Very few children and teenagers are Pure Evil. Most villainous children are especially portrayed as naïve and not knowing right from wrong. However, Juvenile Delinquents can qualify if they already know what they're doing is wrong yet choose to do it anyway (e.g. Henry Evans, Joffrey Baratheon and Emma Grossman).