Young Creature (5e Template)
From D&D Wiki
A creature qualifies for the "Young Template" when its age is less than 90 % of its race's "Age of Adulthood" listed in their respective descriptions. For Example, a Human is considered young at the age of 16 and lower (From the middle teens down), whereas an Elf is considered young before the age of 90.
The creature's statistics don't change, except for their abilities, languages, and skills. Recalculate the creature's Challenge Rating accordingly to adjust for these changes:
Abilities. A Young creature has more natural agility and an untapped source of physical energy, but is green to the ways of the world. A young Creature's Dexterity increases by 4, and their Constitution is increased by 2; however, all mental statistics (Intelligence, Wisdom, Charisma) are each decreased by 2.
Languages A young creature loses one Language proficiency, with the exception of their own racial language.
Skills A Young creature loses one skill proficiency.
Reactive A young creature gains a +2 bonus to their Initiative rolls.
Reduced Size A young creature's size is one category smaller than the base size of its respective race. This can change what equipment a creature may be able to use effectively. A Small creature has disadvantage on attack rolls whenever he uses a Heavy weapon. A Tiny creature, however, cannot use Heavy weapons at all, and has disadvantage to attack rolls whenever he uses a Versatile weapon.
A young creature's actions do not change.
Recalculate the creature's CR based on the new abilities, skills, languages, and size.