My little guy started at 4 years and 11 months. He would have gone crazy if he had an extra year at home. He was so excited about going and he was so ready for it. He's settled in really well and he's pretty much the same age as all the other little folk in his class. He was in pre-school last year and when I asked his teacher about holding him back for a year she had a bit of a giggle at me and told me that he was ready so I went with her judgement since she's the professional. My other little guy was one of the youngest in his class because he started under a different system and he has had no trouble. On the contrary, his teachers have never had anything that wasn't positive to say about him, he's excelling in maths and public speaking and he takes a leadership role whenever he can. Another little girl that was in his class who is older than him has been held back to repeat kindy so really it comes down to the individual child.
I think that holding a child back who is school ready just because you want them to be the oldest is silly. There isn't much benefit in being the oldest and it would be a bit depressing being the same level as kids who are a year younger. That said I think sending a child who isn't ready just because they are eligible is silly too.

The NSW education department used to have a school readiness check-list. It was stuff like being able to put their shoes on and their own clothes and being able to raise their hand to ask a question if they needed to and cutting in a straight line and so on. IMO if they tick all the boxes on the school readiness then you send them and if they don't then you keep them back.
Yep I agree with Onyx. I think it depends on your child and sometimes some boys aren't ready til another year later due to how they develop differently to girls too. I really think it's a very individual basis and decision only a parent can make and at the age of 2, we don't really know when our child is going to be ready just yet kwim?