Assuming the date field is in position 1-8, you can code the following step prior to your job:
//SORT1 EXEC PGM=SORT,PARM='CENTWIN=80,NULLOUT=RC4'
//SORTIN DD DSN=INPUT.FILE,DISP=SHR
//SORTOUT DD SYSOUT=*
//SYSOUT DD SYSOUT=*
//SYSIN DD *
If the header date matches the current system date, you should get RC=0. However, if it does not match, a RC=4 should be produced.
Then you can code COND=(0,NE,SORT1) on the EXEC statement of the following step(s). This instructs the next STEP to only execute if SORT1 got a RC=0. If SORT1 did not get a RC=0, then the following step(s) will be bypassed.