DD1 started YR aged 4yrs 1 month, part time from September - Easter. She was more than ready for it.
DD2 started P1 (moved to scotland) aged 4yrs 10months and would have probably benefited from staying at nursery longer, as still struggles with her reading and writing as we near the end of P2.
DS is due to start school this year. We will be moving back south, so will start YR in September aged 4yrs 10months. Im not sure he is ready to be honest, he is still very much a toddler, and is undergoing SALT to help with his speech issues.
The one bonus I see by moving the kids back south this summer, is that in effect DD2 will repeat a year. She would be going into P3 this summer if we stayed here, but she will be going into Y2 in England. I think she needs it! It will hopefully give her a chance to solidify the skills she is learning at the moment, without the "rushing through the syllabus" that her current teacher admits to!
In an ideal world, I think there shouldnt be an "age" at which children start school, more a "level" at which they will be able to deal with what is expected of them in school.