If it's only 3 days a week it's kinder (or how I understand kinder) and I would send him. Especially if his carers agree he is ready in all ways. It's not just about a child being bright. I went to big school when I was only 4.5, the academic side wasn't a problem but the social side you could see differences. There was one other girl same age as me and we were bestest buddies. It's not like we were singled out or felt different - we were still laughing at poo jokes and couldn't sit still...
I'm a fan of holding them over till later (for big school, uniforms, 5 days a week).

