i want to change the value of the field (name) of the model(categ.age) based on the value of the field (age) that belongs to the modele(mod.age) 

i declared a One2many relation between the models like the code bellow and i used a related field but the value still not take in consideration the changing value 

                class age(models.Model):

                _name = "mod.age"

                category = fields.Many2one('categ.age', 'group of age')

                name_test = fields.Char(compute="set_age_group", related='category.name')

                age = fields.Integer('Age')

              @api.depends('age')

              def set_age_group(self):

                    if self.age < 20:

                        self.name_test = 'type2'

                   else:

                       self.name_test = 'type3'

             class cat_age(models.Model):

             _name = "categ.age"

             _description = "group of age"

            name = fields.Char(string="Name of categorie", store=True, readonly=False)

            other_field = fields.Char(string="other_field")