currently doing Car Rental Service as a project

how exactly would I get an age validator and a rental cost calculator to work (python tkinter)?
the code I used for the age validator is as follows:

def validate_age():
    dob = dob_entry.get()
    age = calculate_age(dob)
    if age < 24:
        tk.Label(text="You must be aged 24 or over to complete this rental form.")
        submit_button.config(state="disabled")
    else:
        tk.Label(text="")
        submit_button.config(state="normal")

and the code for the rental cost calculator is as follows:

def calculate_cost():
    global rental_cost
    # Calculate rental cost based on duration
    if rental_label_days >= 1:
        rental_cost = 30 * rental_label_days
    elif rental_label_weeks >= 1:
        rental_cost = 95 * rental_label_weeks
    elif rental_label_months >= 1:
        rental_cost = 270 * rental_label_months

    # Add VAT to rental cost
    rental_cost = rental_cost + (rental_cost * 0.2)
    # Update the cost label
    cost_label.config(text="Total cost: " + str(round(rental_cost, 2)))

but the error i get when I try to use these are as follows:
age validator:

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\corey hopkins\AppData\Local\Programs\Python\Python311\Lib\tkinter\__init__.py", line 1948, in __call__
    return self.func(*args)
           ^^^^^^^^^^^^^^^^
  File "C:/Users/corey hopkins/Documents/IT Unit 4/Car Rental Form.py", line 56, in validate_age
    submit_button.config(state="disabled")
    ^^^^^^^^^^^^^
NameError: name 'submit_button' is not defined

rental cost calculator:

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\corey hopkins\AppData\Local\Programs\Python\Python311\Lib\tkinter\__init__.py", line 1948, in __call__
    return self.func(*args)
           ^^^^^^^^^^^^^^^^
  File "C:/Users/corey hopkins/Documents/IT Unit 4/Car Rental Form.py", line 17, in calculate_cost
    if rental_label_days >= 1:
       ^^^^^^^^^^^^^^^^^^^^^^
TypeError: '>=' not supported between instances of 'Label' and 'int'