At what age do babies start reading?

That range is wide for a reason. Children develop at genuinely different rates, and the word "reading" covers a lot of ground, from recognizing that a McDonald's sign says something, to sounding out letters, to pulling meaning from a sentence on their own.

What the stages actually look like

In the first year, babies are not reading but they are doing the groundwork. They are learning that sounds correspond to things, that symbols carry meaning, that a book is an object you interact with. That is not nothing.

Around 18 months to 2 years, many children start recognizing their own name in print and a handful of high frequency words they have seen repeatedly. This is sometimes called environmental print awareness, and it is the first real foothold.

Between 3 and 5, most children begin understanding that letters map to sounds, which is called phonemic awareness. They start sounding things out, guessing at words from context and pictures, and memorizing short books they have heard many times.

Formal decoding, reading new words they have never seen before by working through the letters, usually clicks somewhere between 5 and 7 for children without reading difficulties.

The thing worth knowing about the range

A child who reads independently at 5 and a child who gets there at 7 are often indistinguishable by 9 or 10. Early reading is not a reliable predictor of later ability. What does predict later reading is how much a child is read to, how many words they hear in conversation, and whether they come to see books as interesting rather than obligatory.

If you are asking because you are worried about a specific child, the most useful single thing is consistent daily reading aloud, well past the age when you might think they no longer need it. Children can listen at a higher level than they can decode on their own for years, and that gap is where vocabulary and comprehension grow.