Why does Boomhauer look young and Hank Dale and Bill look so much older than him? Because there all supposed to be around the same age arent they?

They all went to high-school together, so yes - they are about the same age. Hank, Dale, and Bill (formerly) were all married. I guess Boomhauer's incessant skirt-chasing keeps him looking young, although he has developed a slight beer gut from hanging out in the alley.