i have age field in my student.student module,this is computed filed according to birthdate field 

but while searching in odoo its not showing because its computed field so i write below code for eneble searching for this field but its not working 

def _search_subscription(self, operator,value):

        a=[]

        b = self.env['student.student']

        for x in b.search([]):

            if x.age==value:

                a.append(x[0])

        return [('id', 'like' ,a)]

i want to return all field which age is like value,please give me solution...