I believe France has made maternelle compulsory from age 3 in recent years.
My eldest is October born - should have been mid September or so. I didn't know about school ages when she was born and was disappointed when I realised she would be old in her year as our family has much history of children thriving young in year, plus we're all tall. We moved her to a school nursery for her 2nd preschool year as we could see she was going to outgrow the daycare she was in - all her friends were heading for school and she was as ready as they were. Had she been within the first 2 weeks of September I would have pushed hard to have her start school early, as it was I accepted asking once and being told no (independent sector).
She's just finished school, done very well; but to be honest I sometimes wonder if her approach to academics might have been different if she'd been stretched by an earlier school start. Ironically, I went through school young ish in year (not UK) but would have benefited by skipping a year had it been allowed when I was young enough (my parents were offered advancing me in year 7 but felt it was too late).
My youngest is summer born (by chance not planning) and I am so grateful that he is - he grew early and in many other ways could have been badly out of place had he been old in year. Two of his close friends by chance are late August and September. At no age would you have correctly guessed which one was nearly a year older than the other two.
I do think it would be good to have a 4-6 month range where there was a choice when to start. Perhaps that is what is being achieved by the greater acceptance of deferred entry nowadays, not sure.
The reason you hear both from those who want a child held back and those who'd like an earlier start, is that there is a range of school readiness and those whose children fall on the optimal side of the cut-off for them, don't have parents worrying about it!