Convert combobox user input in to date with tkinter

[Ame]

This is my code right now:

from datetime import datetime
from tkinter.ttk import *
from tkinter import *
from openpyxl import *


class Application(Tk):
    def __init__(self, *args, **kwargs):
        Tk.__init__(self, *args, **kwargs)

        d29 = list(range(1, 30))
        d30 = list(range(1, 31))
        d31 = list(range(1, 32))

        self.months = dict(
            January=d31,
            February=d29,
            March=d31,
            April=d30,
            May=d31,
            June=d30,
            July=d31,
            August=d31,
            September=d30,
            October=d31,
            November=d30,
            December=d31)

        self.lbl_birth = Label(self, text="Birthday:", font=('times', 14))
        self.lbl_birth.grid(row=1, column=1)

        self.cb_day = Combobox(self, values=self.months["January"])
        self.cb_day.grid(row=1, column=2)
        self.cb_day.set("1")

        self.cb_month = Combobox(self, values=[*self.months])
        self.cb_month.bind('<<ComboboxSelected>>', self.update)
        self.cb_month.grid(row=1, column=3)
        self.cb_month.set("January")

        self.cb_year = Combobox(self, values=list(range(1996, 2006)))
        self.cb_year.grid(row=1, column=4)
        self.cb_year.set("2000")

        day, month, year = self.cb_day.get(), self.cb_month.get(), self.cb_year.get()
        mydate = datetime.strptime(f'{day} {month} {year}', '%d %B %Y')
        today = datetime.now()
        years = today.year - mydate.year

        
    def update(self, event):
        self.cb_day["values"] = self.months[self.cb_month.get()]
        self.cb_day.set("1")


if __name__ == "__main__":
    app = Application()
    app.title('My Birthday App')
    app.mainloop()

Thank you