Validation: how to prevent form progress based on conditions?

I have the form programmed where if the user enters a specific age and chooses a specific class, an error message will appear. Now, I am trying to prevent the use from continuing on in the form if any error message occurs. Thanks for the help.

I can assume that your form is set up to show error message created with text element, is this correct? You can add an action to hide Submit button or Page Break elements into conditional statements that are showing error message, for example:

We will gladly assist if you need any further help.