Boomerang caters more to popularity and less to overt nostalgia than it used to. Duck Dodgers is an established popular show, never mind that it only went off the air a little while ago; therefore, it is Duck Dodgers they broadcast.
His real name could be Porky Pig, but he just gets called Eager Young Space Cadet because that's what he is. In the military, soldiers are frequently referred to by their rank (soldier, private, sergeant, etc.), so his rank could be Space Cadet and so he gets called that, and the Eager Young is just added on.
Perhaps the adjective is a sub-ranking within the broader rank of Space Cadet... because it's in SPACE! You'd start out as a Hopeful Trainee at Space Academy, then advance to Wide-Eyed Young Space Cadet, Eager Young Space Cadet, Plucky Space Cadet, and so on up the ranks to Daring Captain, Adventurous Captain, and Fearless Captain.) Aw, I Made Myself Sad now that Real Life military titles are so bland.
In the episode where Cadet touches Moognesiam and becomes a huge buff steroid fueled mass of muscle. I notice in one scene he rips his shirt off revealing two large nipple piercings. Does that mean that cadet actually wears giant nipple rings on a regular basis? This could go into nightmare fuel...
How this show ever got cancelled. Were the people in charge of Cartoon Network at the time afraid of money and/or success?