The episode "The Secret(s) of Castle McDuck!" gives their birthday as April 15th. The final digit of the year is obscured out, but it was between 2000 and 2009, approximately 10 years before the show's events.
Huey (red): the eldest triplet (by 3 seconds). He's knowledgeable, nerdy, excitable, and is an enthusiastic Junior Woodchuck.
Dewey (blue): the middle triplet. He's brave, adventurous, and loves to be the center of attention.
Louie (green): the youngest triplet (by 48 minutes). He's laid-back, lazy, smooth-talking and loves money, but he is also sharp (seen in the episode "The Most Dangerous Game ... Night")