Each child is unique. It is difficult to describe exactly what should be expected at each stage of a child's development. While certain behaviors and physical milestones tend to occur at certain ages, a wide range of growth and behavior for each age is normal. These guidelines show general progress through the developmental stages rather than fixed requirements for normal development at specific ages. It is perfectly natural for a child to reach some milestones earlier and other milestones later than the general trend.
If you have any concerns about your child's own pattern of development, check with your healthcare provider.