Steppemum thinks that reading ?averages out by 10, regardless of when you start?.
This is true of most of Europe, but not the UK. In other European languages learning to read is much easier and takes very little time, because in none of them do identical letters or letter strings keep having different pronunciations, like ?on ? only, once, other?. The occasional recently imported word from another language may not be completely decodable, but 99.9% are.
In English 69 spellings have more than one sound, as I have shown in one post on englishspellingproblems.blogspot.com Those phonics inconsistencies result in over 2000 tricky-to-read words which I have listed on the Sight Words page of www.EnglishSpellingProblems.co.uk Because of those words, roughly 1 in 6 English-speaking children never learn to read properly.
Those 2000 sight words take some learning, so children who are able and willing to start learning to read English early have a huge advantage. But the worst thing anyone can do is push their children into reading before they are ready.
Children vary greatly in their reading-readiness. Helping them to become so is the most important thing parents can do, apart from helping with decoding the tricky words like ?could, should, would, oh, people, come, do...? once they become keen to learn.
The best way to learn to read English is still to read to an adult and be helped to decode the tricky words, until they become automatic. This can be trying and stressful for both children and parents, and with some children requires enormous amounts of patience (as I know from having to go over and over again, with my son, the tricky words which kept tripping him up and his teacher used to write on little cards for practice at home).
The main point I want to make (having studied Lithuanian, Russian, English, German, French, Spanish and Italian) is that learning to read English is exceptionally difficult because of the way it is spelt. So it's not surprising that it pre-occupies teachers and parents for ever and ever.