If there is a correlation between the age of schoolchildren and their reading comprehension, you could speculate about the basis for this relationship. probably the most reasonable speculation is that

Yes, I believe there is a general relationship between the school age and reading comprehension. Younger children may read at an early age but the lack of social experience to associate words with concepts becomes difficult for children to decode. Unlike children who are older or at children at the right age, can better read and understand the text, provided that there is an initial guide to reading.