oracle - Checking if beneficiary is adult (more than 18 year) when inserting -

in "beneficiary" table have "birthdate" column, when beneficiary registered, want check, if not adult (no more 18 year), want disallow register

for example today "2017-04-05" , if beneficiary tries insert birth date "1999-04-06", want disallow insert. if birth date "1999-04-05" or earlier, insert must happen.

after searched found trigger this? tried several ways not realized how add restriction table.

you can use this:

(if never update birthdate column, can remove piece: or update , recreate trigger )

create trigger trg before insert or update on beneficiary each row begin     if :new.birthdate >  add_months(sysdate , -12*18)         raise_application_error(-20001, 'underage user');     end if; end;