Does "perfect" imply never having changed? Does the Bible say so?

**"God is perfect"** is often used as a justification for the belief that God never became God, but that rather, He never changed, but simply always was God, and **always was perfect**. What is the Biblical justification for the claim that "perfect" means that God always was God and never changed, seeing as Jesus commands us to be perfect, "even as our Father in Heaven is perfect"?