SELECT pokupatel FROM humans WHERE date_rojdenia BETWEEN 10 and 50;

DATE_SUB(NOW(), INTERVAL 10 YEAR)

DATE_SUB(NOW(), INTERVAL 50 YEAR)

SELECT pokupatel FROM humans WHERE date_rojdenia
   BETWEEN DATE_SUB(NOW(), INTERVAL 50 YEAR)
       and DATE_SUB(NOW(), INTERVAL 10 YEAR);

SELECT pokupatel FROM humans WHERE date_rojdenia
BETWEEN UNIX_TIMESTAMP(NOW() - INTERVAL 50 YEAR) and UNIX_TIMESTAMP(NOW() - INTERVAL 10 YEAR);