?Monkey D Luffy is currently 19 years old.
He was born on May 5th, in the year 1977 in the Alternate timeline. Luffy’s age is intentionally significant throughout the series as he strives to become the Pirate King, and the youngest who has done so. Luffy starts his adventure a young boy, but over the course of the story matures to the age of 19 through the events of The Water Seven Saga.
This places his age as currently 19 years old.