If it's never old, it's always GNU.

*waits for the groans of disgust and dismay* ;D

I didn't accept answers like 'chick', 'calf', 'foal', etc. for two reasons.

One, because these are only one life-stage in the life of an animal which does grow old.

Two, it misses out on the fact that this is a "silly riddle," which should tell you I'm looking for something less "serious."

I did accept, for full credit, yoi55's answer KID (a baby goat) because it was somewhat pun-ish, and so fit the riddle idea.