Usually when my DS4 imitates, it is more like he is learning/copying mode.
For example, DS has learned many songs at school. When he learns one that I or DH doesn't already know he will teach it to us, much in the same manner his teacher probably does it. He'll sing a line and then say, "OK, now you sing it (back to me)". Then he'll add on one line at a time until he has taught us the whole song.
Lori - I know what you mean about the "class clown" it isn't full blown yet but my DS does have those tendencies at school and in other group settings.
As for imitation/impersonation: Billy Crystal mentions in his memoir, 700 Sundays, that he started his impersonations quite young. At about 5 yrs I think.
