don´t recognize variable of php

Question

I have the following code in two files separately

file one.php

   Age: 

        

Answer 1

It's not recognized because you don't create it. Variables don't magically appear in PHP¹. You need to get that value from the $_POST superglobal:

¹ Anymore. They used to when register_globals existed. But that has been obsolete since long before you started coding.