Is 5 too young?

Hi all! My 4 year old turns 5 on August 18th and the schools enrollment age is 5 by September 30th. My question is, even if my son is pretty smart is it a bad decision to send him to school so young? I’ve heard mixed reviews. “Hold him back he’s too immature for his peers” or “he’s bright and smart he’ll be fine”. Looking for advice from experience. TIA!