Incorrect spelling, definition: this word is spelled incorrectly because the plural of twenty should be created with a different ending. All because there is a rule in English according to which any noun containing a consonant before the letter -y must be inflected by replacing the letter -y with -i and adding the suffix -es. Therefore, twentys is the incorrect form and twenties is the correct one.

Correct spelling, definition: twenties is a plural of twenty. It’s often used in reference to age, an era, or temperature. This form is the only correct one, because when we have a word with a single consonant before the last -y, we must change -y to -i and then add the suffix -es in order to create a plural. That’s why the right spelling is twenties, not twentys.

Definition of twenties:
noun, the decade between 20 and 29 in any century, usually 1920–1929
God, I really wish I was born in the twenties; I love the fashion of that time!
My great-grandmother lived in the twenties.