How to validate if clients age is >= 18 and whats the proper way of validating the fields

Question

Whats the best way to check if a clients age is >= 18 and whats the best validation method for the fields!

I have tried some different methods but all of them have errors!

Most of these implementations i have found them on this site or by reverse engineering the Django's UserCreationForm

Is this way that i am doing it the "correct" but i am missing something or there is a better way?

Register Form

class AccountCreationForm(forms.ModelForm):
    username = forms.CharField(
        label='Username',
        widget=forms.TextInput(
            attrs={
                'class': 'form-control',
                'placeholder': 'Enter username',
                'id': 'registerUsernameInput'
            },
        ),
    )
    email = forms.EmailField(
        label='Email',
        widget=forms.TextInput(
            attrs={
                'class': 'form-control',
                'placeholder': 'Enter email',
                'id': 'registerEmailInput'
            },
        ),
    )
    password1 = forms.CharField(
        label='Password',
        widget=forms.PasswordInput(
            attrs={
                'class': 'form-control',
                'placeholder': 'Enter Password',
                'id': 'registerPassword1Input'
            },
        ),
    )
    password2 = forms.CharField(
        label='Confirm Password',
        widget=forms.PasswordInput(
            attrs={
                'class': 'form-control',
                'placeholder': 'Confirm Password',
                'id': 'registerPassword2Input'
            },
        ),
    )
    date_born = forms.DateField(
        widget=forms.SelectDateWidget(
            years=[x for x in range(1940,timezone.now().date().year + 1)],
            attrs={
                'class': 'form-control',
            }
        )
    )

    class Meta:
        model = Account
        fields = ['username', 'email', 'password1', 'password2', 'date_born']

    def save(self, commit=True):
        user = super(AccountCreationForm, self).save(commit=False)
        user.username = self.cleaned_data.get('username')
        user.email = self.clean_email()
        user.password = self.clean_password2()
        user.date_born = self.clean_date_born()

        if commit:
            user.save()
        return user

    def clean_password2(self):
        password1 = self.cleaned_data.get('password1')
        password2 = self.cleaned_data.get('password2')

        if not password2:
            raise ValidationError("You must confirm your password")
        if password1 != password2:
            raise ValidationError("Your passwords do not match")
        return password2

    def clean_email(self):
        email = self.cleaned_data.get('email')
        if Account.objects.filter(email=email).exists():
            raise ValidationError('Email already exists')
        return email

    def clean_date_born(self):
        date_born = self.cleaned_data.get('date_born')
        if timezone.now().date() - date_born < timezone.timedelta(6574):
            raise ValidationError('You are under 18.')
        return date_born

Register View

def register_view(request):

    # Redirect the user if already logged in
    if request.user.is_authenticated:
        return redirect('main:homepage')

    if request.method == 'GET':
        form = AccountCreationForm()
        return render(request, 'main/register.html', {'title': 'Register', 'form': form})

    if request.method == 'POST':
        form = AccountCreationForm(request.POST)
        if form.is_valid:   
            user = form.save()
            login(request, user)
            return redirect('main:homepage')


        messages.error(request, 'Form not valid') 
        return redirect('main:register')

Answer 1

If you want to validate the fields of a model then you can use validators. https://docs.djangoproject.com/en/2.2/ref/validators/

def validate_age(age):  
    if age <= 18:  
        raise ValidationError(_('%(age) should be more than 18'), 
        params= {'age':age},) 

OR if you want to validate the form field then you can use cleaned_data like: In your forms.py inside the class you can define a function:

def clean_fieldname(self):  
    field_content = self.cleaned_data['field_name']  
    #validate the field here and raise Validation Error if required  
    return the field_content 

As per my recommendation validation at form level is much better.