In England and Wales, legally at five, but practically most children go to school at four, having been at nursery school since the age of three (as it is free from that age).
A child here has to be named by 1 year and 42 days after birth; so jiggeryqua was wrong in suggesting that a child could remain unnamed to school age.
My point was that the three things you stated as making it necessary for a child to be named immediately at birth (medical insurance, tax returns, social security number) - and suggesting any country which didn't require such things was "bizarro world" - aren't necessary for newborns in the UK. We have the NHS, and our tax and social security system is quite different. Perhaps you didn't mean to be insulting to other cultures, but it certainly smacked of USA or the highway.
All my children were named shortly after their births and in two of the four births we didn't have a settled name planned, and in one case we changed what we had decided after the child was born as he "looked like" a Charles, not a Robert as we had planned.