Children are not aiming to reach or surpass some level of language or some time frame that someone else set for them. They are competing only with themselves, on their own terms. The child whose speech is most advanced at the age of 2 is not necessarily going to be a higher achiever at age 20 than the child who was slower to learn language. Language is only part of what children have to learn and a child who seems slower might be learning in a different way, or concentrating on other things.
Children won't learn anything which they are not ready for -- they may parrot things that you or someone else tries to 'teach' them, but a parrot only learns to parrot. What your child is ready for is not found in books or in someone else's children. It's found in your child, and to learn about your child you must also give yourself -- and your child -- time. Your children are as new to you as everything they are learning about is to them.