krileon wrote: If this is date of birth for the user themselves you don't need that. Suggest just using the following parameters on the date field to restrict how old they can select.

Minimum Year: - 100
Maximum Year: -13

That should limit them to the age range of 13 - 100. Nothing else will be selectable. Both parameters can be found under Parameters > Validation of your date field.

If you still insist on custom validation then some comments regarding your code is it's not valid PHP or substitutions. The code field simple takes your string of text, converts to PHP, and executes it; please also read the parameter description carefully regarding what values your code should return for validation purposes.

For simple display of PHP, yes. For validation, no. Code Validation just executes your supplied PHP where you'd return a true or false if the value is valid; please be sure to read the parameter descriptions carefully.