As with all areas of development, children begin to recognize numbers and letters at different times. However, most children begin to recognize familiar letters, such as the letters in their name, around age 4. As they enter kindergarten, they will begin to learn all the letters and numbers as well as be able to identify the sounds each letter makes.
It is important for all children, no matter their current developmental level, to be exposed to letters and numbers through books, signs, magazines, and so forth. Show your child that the words you are reading are made up of the different letters they are seeing on the page. Make up rhymes, and read rhyming books to help them better understand the sounds each letter makes.
Help develop a love of reading and books in your child by making reading a priority for your family. Your child will begin to learn about letters and numbers in preschool; however, the time spent learning through fun reading activities at home will help your child learn the skills for reading even faster.
The age range really varies. Practice is always good. Some children recognize alphabets and numbers at very early ages. Others, might learn between the ages of 3 and 5. Do not worry. Playing games using numbers and alphabets is a good start.