Intellectual disability is a type of disability that includes many social and practical skills, is characterized by limitations in both mental functions and adaptive behaviors, and occurs before the age of 22 (Schalock, Luckasson & Tassé, 2021). According to this definition, updated in 2021 by the American Association on Intellectual and Developmental Disabilities (AAIDD), there are various perspectives on the age of onset of the disability, the continuation of brain development until the 20s, and the end of the developmental period. It has been increased to 22 years because of its angles (Schalock, Luckasson & Tassé, 2021).
References
Schalock, R. L., Luckasson, R., & Tassé, M. J. (2021a). Intellectual disability: Definition, diagnosis, classification, and systems of supports, 12th Edition. American Associaton on Intellectual and Developmental Disabilities. https://www.aaidd.org/intellectual-disability/definition