How did Crabb and Goyle get to be Death Eaters?

[pbeider]

No: HPFGUIDX 33219

This is the second of two questions I (a newbie) did not find 
addressed in the "Mysteries and Inconsistencies FAQ":

Near the end of Book 4, Crabb and Goyle are among the Death Eaters 
Voldemort talks to individually; he says something about them doing 
better "next time."  But if they're close to Harry's age, they 
couldn't have done any work for Voldemort before his disappearance.  
Is it plausible that they would have had enough knowledge of 
Voldemort's revival to have signed on as Death Eaters since then??