There is no single answer to this question as different children will be ready for chapter books at different ages. However, as a general guide, most children will be ready for chapter books around the age of six or seven.
At this age, children are usually able to read independently and have a good attention span, meaning they are able to concentrate on a longer story. They will also likely have a good understanding of basic grammar and vocabulary, which will be necessary for understanding chapter books.
If your child is interested in reading chapter books, it is a good idea to encourage them. starting with shorter ones and gradually working up to longer ones. There are also many excellent series of chapter books aimed at young readers, such as the "Harry Potter" and " Percy Jackson" series, which can be a great way to get them hooked on reading.