Calculadora de Edad

Años completos cumplidos:
=DATEDIF(A2, B2, "Y")

Meses del residuo (sin contar los años):
=DATEDIF(A2, B2, "YM")

Días del residuo (sin contar meses ni años):
=DATEDIF(A2, B2, "MD")

Total de días vividos:
=B2-A2

Día de la semana (1 = domingo … 7 = sábado):
=WEEKDAY(A2)

Días hasta el próximo cumpleaños:
=IF(DATE(YEAR(B2),MONTH(A2),DAY(A2))>=B2,
    DATE(YEAR(B2),MONTH(A2),DAY(A2))-B2,
    DATE(YEAR(B2)+1,MONTH(A2),DAY(A2))-B2)

-- PostgreSQL — AGE()
SELECT
    birth_date,
    AGE(CURRENT_DATE, birth_date)                         AS age_interval,
    EXTRACT(YEAR FROM AGE(CURRENT_DATE, birth_date))      AS age_years,
    EXTRACT(MONTH FROM AGE(CURRENT_DATE, birth_date))     AS age_months,
    EXTRACT(DAY FROM AGE(CURRENT_DATE, birth_date))       AS age_days,
    CURRENT_DATE - birth_date                              AS total_days
FROM people;

-- MySQL — TIMESTAMPDIFF
SELECT
    birth_date,
    TIMESTAMPDIFF(YEAR, birth_date, CURDATE())   AS age_years,
    TIMESTAMPDIFF(MONTH, birth_date, CURDATE())
        - TIMESTAMPDIFF(YEAR, birth_date, CURDATE()) * 12
                                                  AS age_months,
    DATEDIFF(CURDATE(), birth_date)               AS total_days
FROM people;

-- SQL Server — DATEDIFF
SELECT
    birth_date,
    DATEDIFF(YEAR, birth_date, GETDATE())
        - CASE WHEN DATEADD(YEAR,
              DATEDIFF(YEAR, birth_date, GETDATE()),
              birth_date) > GETDATE()
          THEN 1 ELSE 0 END                       AS age_years,
    DATEDIFF(DAY, birth_date, GETDATE())           AS total_days
FROM people;