Convert combobox user input in to date with tkinter

[Ame]

from datetime import datetime

day, month, year = ('1', 'January', '2000')
mydate = datetime.strptime(f'{day} {month} {year}', '%d %B %Y')
print(mydate)
today = datetime.now()
print(today)
years = today.year - mydate.year
print(years)

Output:
2000-01-01 00:00:00
2020-06-29 22:21:04.644274
20

Thanks! That worked, but I'm only getting the date based on 2000-01-01. When I try to change the month it gives me back this error:
"Exception in Tkinter callback
Traceback (most recent call last):
File "C:\Program Files (x86)\Python38-32\lib\tkinter\__init__.py", line 1883, in __call__
return self.func(*args)
TypeError: update() takes 1 positional argument but 2 were given"
How can I get the all the age and the birthday that may be inserted?
Thanks again