Why not just TELL the compiler what length your WANT to use for the new variables instead of forcing it to guess?
data scoredata2;
set scoredata0;
length gender_ac $21 gender_char $8;
gender_ac = gender||'/'||gender_code; /*auto*/
gender_char = put (gender_code, 8.); /*put*/
run;
SAS will use the BEST12 format when you let it auto convert a number into a string. So the values of GENDER_AC will be the length of GENDER (is that 1 byte? 6 bytes? Something else) plus 1 plus 12. Whether SAS is smart enough to figure that number out or whether it just use 200 you would have to run it and see. For the second step the values will all be length of 8 bytes. I would assume the compiler could figure that out and define gender_char as length $8 since that length is known at compile time based on the width of the format used in the PUT() function call.