The "age as of date" calculates the birthdate range for the cohort.
A client's immunization status, for the purposes of assessing up-to-date status, is determined by the "assessment date." Immunizations administered after the assessment date will not be considered when determining if a client is up-to-date.
For example, if you want to assess children 2-4 years as of 1/1/2025, you would set the age as of date as 1/1/2025. If you want to only consider immunizations administered on or before 1/1/2025 you would set the assessment date as 1/1/2025.