UPDATE
    st156
SET
    st156.date = TO_DATE(SUBSTR(birthday_date, 1, 6) || '19' || SUBSTR(birthday_date, 7, 2), 'DD MM YYYY')
FROM
    st156
WHERE REGEXP_LIKE (birthday_date, '[0-9]{2} [0-9]{2} [0-9]{2}');

UPDATE
    st156
SET
    st156.date = TO_DATE('01 01 19' || birthday_date, 'DD MM YYYY')
WHERE REGEXP_LIKE ( birthday_date, '[0-9]{2}') AND LENGTH(birthday_date) == 2


Select st151.year_of_birth, count(st151.year_of_birth) as Prirost from st151 group by year_of_birth order by year_of_birth