Russian children begin to read an write some time before the school (I did at about 5 years old, and then went to school at 6). As for the proficiency age, it is mainly a question of methodologies, which are rather ineffective. I often joke that children these days spend 11 years learning how to spell words and put commas properly—a time enough for a non-native speaker to become reasonably fluent in Russian. Which is only partically a joke, because many people never become good at writing. I hope this is going to change, because recently they started to teach Russian at school (and I mean, real Russian, not just spelling and punctuation). As for how much time a sane person needs... - starting with the 3rd grade, it is assumed that a pupil can read everything they need. 4th grade is the last where the reading skill is tested — which essentially means that no one bothers to test the efficiency of your reading if you are older than 10. - participles are taught in the 7th grade, which mostly concludes the course of Russian at school (I means, there is little else to learn). When I was a child, the 8th grade was the last that included Russian classes. And I must admit it was enough for me and children I studied with. - these days Russian is taught not for 7-8 but for the whole duration of 11 years. Given how poorly students perform at the state-level official test, I cannot help but question the efficiency of the current program.

All life. But just learning letters takes 1 year, but i was member of education experiment of reduction basic education (3 years instead of 4 years), now they refused the reduction. So, a child after 1-2 years in school can read and write anything with mistakes. Studying in school begining from 7 years old, but often parents (or in kittengarden) teach children read and write letters. So all depends on a child and his teacher. For example, my brother teached (he great teacher ahahaha) me read and write cyrillic and latin in print letters for 1 summer, when i was 5 y.o.

To my son 6 year old and his how learning read. but there are children who read very well.

I can answer only about Bulgarian children but I hope it will be helpful too, since Bulgarian has even more phonetically consistent spelling. It's quite usual for children to learn reading and writing some years before even entering schools' first grade (at 6). They learn it through parents, in children gardens (through simple games), or even only by itself. Not long ago I had a text chat in internet with a boy (a 5 years old child of a friend of mine). I was assured by his parents that he hasn't been taught to read and write by any means. I was amazed that he managed to write at least three times faster than I do! (:D) and his only mistakes were with some letters, which in speech are nearly indistinguishable ( 'в' at the end of the word -> 'ф') ... in fact, he was just writing phonetically the way he heard the words, without knowing any grammar or rules. Of course it's different in each case - at these ages it's not easy to force children to learn anything. Hopefully, nowadays computers and internet are a part of their life and the literacy is something they learn quite naturally.