Below formula can be used to calculate age from date of birth in Salesforce –

IF(
NOT(ISNULL(BirthDate)), /* Condition to check to make sure BirthDate is not null */
TEXT(FLOOR((TODAY()-BirthDate)/365.2425)) & " year(s) " &
TEXT(FLOOR(MOD((TODAY()-BirthDate),365.2425)/30)) & " month(s)", /* Value IF True */
"" /* Value IF False */
)