There was never any mention of ages in any Canon stories. The Clone Wars TV series simply mentions that Savage and Maul were brothers. However, there is a comic book in the Legends continuity that mentions that Savage is slightly older. Since nothing has been said to counter this in Canon, we can assume it’s true in the current story. However, the story of Savage and Maul has been retconned a few times over the years in books and comic books. So, you always need to take things like this with a pinch of salt.