Here’s one for the ages — or at least the current AP style rule for how to say how old something or someone is. (Sorry, couldn’t help it.)
Guidelines for writing ages
– For people and animals, always use numerals.
Little Johnny turned 4 years old today.
Sparky, the oldest golden retriever in the world, is 19 years old.
– For all other nouns (including products), write out numbers less than 10.
My MacBook Pro is four years old.
This book is three years old.
– Use hyphens for ages expressed as modifiers (before a noun) or as substitutes for nouns.
Their 2-year-old daughter usually has tantrums before bedtime.
This birthday party is for 5-year-olds.
– Use numerals when expressing age ranges as decades (see example). Do not use apostrophes.
I cringe when I see men in their 60s dating women in their 20s (and vice versa).
– When the context does not specify, the age is presumed to be years. Also, write out the number if it starts a sentence.
I’m 50! Fifty years old…