How can I show in UI a configurated restriction message ?

Hi to all ( Bonita 7.1.3 with Windows )

I see that if I use a BDM object in a task without a form, if I configure a Restriction in Contract for a field of the object, if the script of validation returns "false", when I execute the task, the message that I wrote at Restriction appears after click in submit button.

If now, I configure a form in the same task ( this form takes directly the attributes of the contract object ), when I execute the task, if the field doesn't pass the validation, the message of Restriction don't appears.

How can I show the message of Restriction in this case ?.

Example of my restriction: a field named "Age" and I don't want values down of 18.

Script:
if ( objBDMInput.age < 18 )
return false;
else
return true;

Restriction message:
Error. Only values over 18.

At UI, I can put over de text field "age", a label with something like "Write 19 or more", but I want use the message of the Restriction.

Thanks.