Compile time
Recall that each SAS Step is separately compiled and executed. Let's follow this thru. When a data step is compiled. Here is the code that the compiler looks at:

DATA POINTER;  
   INPUT @1  ID       3.  
         @5  GENDER  $1.  
         @7  AGE      2.  
         @10 HEIGHT   2.  
         @13 DOB      MMDDYY6.;  
FORMAT DOB MMDDYY8.;  
DATALINES;