How is developmental disability defined in relation to age?

Developmental disability is typically defined as a chronic condition that causes restrictions in physical, cognitive, or behavioral areas of development. In most cases, it is defined as occurring before the age of 18. This is because the first 18 years of life are considered critical for a person's development and any limitations or delays during this period can greatly impact their overall development. As for the other options, B is incorrect because it extends the age range to 21, which may be true for some specific disabilities, but not for developmental disabilities as a whole. Option C is also incorrect as it implies that developmental disabilities only occur after the age of 18, which is not the case. Option D is not a specific enough answer and does not provide any understanding of when developmental disabilities are typically diagnosed.