This is also possible

@api.multi
@api.depends('birthday')
def _compute_age(self):
    for record in self:
        if record.birthday and record.birthday <= fields.Date.today():
            record.age = relativedelta(
                fields.Date.from_string(fields.Date.today()),
                fields.Date.from_string(record.birthday)).years 
        else: 
            record.age = 0

Thanks.

 iWesabe

#use relativedelta to calculate age in years , months and days
from odoo import api, fields, models
from datetime import date, datetime
from dateutil.relativedelta import relativedelta
@api.depends('dob')
@api.multi
def _cal_age(self):

if self.dob:
 years = relativedelta(date.today(), self.dob).years
 months = relativedelta(date.today(), self.dob).months
 day = relativedelta(date.today(), self.dob).days

self.age = str(int(years)) + ' Year/s ' + str(int(months)) + ' Month/s ' + str(day) + ' Day/s'

Hi

@api.depends('birthday')
    def _get_age(self):
        for r in self:
            if r.birthday:
                bdate = datetime.strptime(r.birthday, "%Y-%m-%d").date()
                today = date.today()
                diffdate = today - bdate

                years = diffdate.days/365
                formonth = diffdate.days - (years * 365.25)
                months = (formonth/31)
                bday = bdate.day
                tody = date.today().day
                if tody >= bday:
                    day = tody-bday
                else:
                    day = 31 - (bday-tody)
                
                r.age = str(years) + ' Year/s ' + str(int(months)) + ' Month/s ' + str(day) + ' Day/s' 
 
age = fields.Char(compute='get_age', string = 'Age')
hope this helps 

class StudentStudent(models.Model):
    _name = 'student.student'

    calc_age = fields.Char(string="Calculated Age", compute="age_calc", store=True)

    # Calculated age
    @api.depends('student_dob')
    def age_calc(self):
        if self.student_dob is not False:
            self.calc_age = (datetime.today().date() -             datetime.strptime(str(self.student_dob), '%Y-%m-%d').date()) //              timedelta(days=365)

Thank You Niyas,

I'm already done like this way ,it's worked.

class BirthDateAge(models.Model):

    _inherit = "hr.employee"

    birthday = fields.Date(string="DOB")

    age = fields.Integer(string="Age")

    @api.onchange('birthday')

    def _onchange_birth_date(self):

        """Updates age field when birth_date is changed"""

        if self.birthday:

            d1 = datetime.strptime(self.birthday, "%Y-%m-%d").date()

            d2 = date.today()

            self.age = relativedelta(d2, d1).years