As I say every time this crops up.....
Yes, in many countries they start later. We are in Italy and they start at 6. Prior to which, they have 3 yrs of semi-compulsory "scuola materna" where, by the time they leave, most of them can read a bit and write a bit and do rudimentary maths.
Once they start elementary school, they have 30 hrs a week. Which is not, in any way, play based learning.They sometimes do creative work, but not very often. They are sitting, at desks, reading, writing and arithmetic-ing. They have anything from 2- 4 hours homework every afternoon which must be done. They are graded, seriously, twice a year. If they fall below a certain standard, you, as the parent, are expected to do something about it, in the form of paying for private lessons.
Last week dd's h/w one day involved writing a composition with a clear introduction, main body and conclusion about her summer holiday, and learning, drawing and labelling the scientific parts of the body of various marine creatures. She is doing addition, subtraction and simple multiplication and division. They have done stuff with the Italian language that I only did with the English language once I became a TEFL teacher. She was 7 on Saturday.
I'm happy with her school, because she is. But I don't think for a second this system is any better than the British one.
So, in effect, what I'm saying is this: I imagine that 4 and 5 yr olds in Britain are doing more or less what 4 and 5 yr olds in Italy are doing. It's just that in Britain they are doing it in school, in Italy they are doing it at nursery. And so on. What dd did in Yr 1 of school, a child in Britain would be doing in Yr 2 or 3.