It explains in the documentation that the default number of variables in a scatter plot matrix is 5 variables. There is an option to use more variables than the default. In addition to the methods you mentioned, the original poster can get the scatter plot matrix he wants out of PROC CORR by looking up the right option in the documentation.
If any of the variables had been category variables, there would have been an error message in the SAS log (as shown below for the NAME variable):
3121 var name age;
ERROR: Variable name in list does not match type prescribed for this list.