While it is not possible to use kintone to automatically calculate an age using the current date as a base, you can calculate an age based on the date a record was updated or a specific date.
An age is calculated by finding the difference between a date of birth and another value. For the other value, use an "Updated datetime" field if you want to calculate an age based on a record's updated datetime, or use a "Date" or "Date and time" field if you want to calculate an age based on a specific date or datetime.

Here, we will describe two methods for calculating an age based on a record's updated datetime: a simplified method that calculates an approximate age without taking leap years into consideration, and a method that calculates an age while taking leap years into consideration.

• Method 1: Age calculation that does not take leap years into consideration
• Method 2: Age calculation that takes leap years into consideration

With this method, leap years are not taken into consideration and a year is considered to be 365 days. An age is calculated as the number of years from a date of birth to an updated datetime. The calculated age may be higher than the actual age.

Place the following fields on the app form in App Settings, and set their field names and field codes.

• "Updated datetime" field
  Field name: Updated Datetime
  Field code: Updated_Datetime

• "Date" field
  Field name: Date of Birth
  Field code: Date_of_Birth

• "Calculated" field
  Field name: Age
  Field code: Age

Set the following formula in the "Calculated" field.
Specify the Number of Decimal Places to Display in the "Calculated" field as 0.

• The "Age" field

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  (Updated_Datetime-Date_of_Birth)/ (60*60*24*365)

The number of years between the updated datetime and the date of birth is calculated, with one year being equal to 365 days.

For information on functions and how date values are treated, refer to the following page.
Calculation of Date, Time, and Date and Time

This method calculates an age as the number of years from a date of birth to an updated datetime, while taking into consideration leap years.

Place the following fields on the app form in App Settings, and set their field names and field codes.

• "Updated datetime" field
  Field name: Updated Datetime
  Field code: Updated_Datetime

• "Calculated" field
  Field name: Updated Datetime A
  Field code: Updated_Datetime_A

• "Date" field
  Field name: Date of Birth
  Field code: Date_of_Birth

• "Calculated" field
  Field name: Date of Birth A
  Field code: Date_of_Birth_A

• "Calculated" field
  Field name: Age
  Field code: Age

Set the following formula in the "Calculated" field.

• The "Updated Datetime A" field

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  DATE_FORMAT(Updated_Datetime,"YYYYMMdd","system")

• The "Date of Birth A" field

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  DATE_FORMAT(Date_of_Birth,"YYYYMMdd","system")

• The "Age" field

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  ROUNDDOWN((Updated_Datetime_A-Date_of_Birth_A)/10000,0)

The updated datetime and date of birth are converted to values in a date and time format using the DATE_FORMAT function, and then the difference between the two values is calculated.
Since the age is represented from the ten-thousands place of the calculation result, the calculation result is divided by 10,000, and then the resulting number is rounded down to the nearest whole number using the ROUNDDOWN function.

For information on the functions used, refer to the following pages.
DATE_FORMAT Function: Specifying the Display Format of Date and Time
ROUND, ROUNDUP, and ROUNDDOWN Functions: Round Off, Round Up, and Round Down Numeric Values