Exactly! All my kids learned at different ages and with some variation in reading programs, teachers’ methods, and parental help. Looking at them today, their current interests and their academic achievement, you would not be able to guess which kids became independent readers very early vs. which began reading relatively later, or which kids mostly taught themselves with a little help from mom vs. which needed much more structured school-based instruction, or for that matter which kids loved reading immediately vs. which enjoyed other pastimes and toys more as a young child.
Ideally, elementary classroom teachers will have the time and training to recognize their individual students’ needs while also providing appropriate instruction to the whole class. In particular, I have friends whose children struggled with undiagnosed dyslexia and other learning differences for far too long before more experienced teachers/literacy specialists recognized there was an issue. So more important than the exact age in which a child learns (and I agree pushing early reading can sometimes do more harm than good for certain kids), I think it is crucial for a primary school teacher to be well-trained to know the difference between a child is not ready to read yet as opposed to a child can’t read for some other reason.