It depends very much what school the area is in and how educated the parents are.
The first time I was made aware of reading ages was when my dd was 5 (in 1974) and the head took me aside on sports day, after the infants had just had their reading tested, and asked if I was aware that she had a reading age of 11. Having grown up in Lithuania where learning phonics is learning to read, reading ages made no sense to me. U could read or u couldn?t.
My dd had shown an interest in learning to read at about age 3 ½ , so we bought a couple of Ladybird books, which she soon found very boring and so we just worked through a few children?s books that she liked instead, until she could read them.
She did ask quite early on, ?Why is there an H in John??. To which I replied, ?It?s just one of the many stupid English spellings that u have to get used to? and she just took them in her stride. She really just taught herself to read, with very little help from me, and has always been an excellent speller too.
Our ds is 2 years younger and learnt to read mainly at school, but they had a system where he used to bring home words which he had trouble with when the teacher listened to him read (said, thought, through...) written out separately on little pieces of card, for us to practise at home. Some of those took a heck of a lot of practice before he could really read them. He took much longer to get into his stride, found spelling much harder too, and I never had any idea what level he was at, but the summer he turned 10 he read the Lord of the Rings.