I need help!!!

I've spent lord knows how long trying to sort out this little problem i'm having with dates in oracle/crystal and if i don't ask for help now i'm going to go insane..

i've written a report to show the last date every employee worked a particular type of shift... but i need a separate/similar report to show the records where the last date was over 6 months ago, and another one (or section within) that shows the results for between 5-6 months ago... where the user inputs what group they want to see the results for...

if you want to see the current code i've got then shout...

otherwise i've tried: "(lastworkeddate") >= {current_date-180}" - but in SQLPlus i'm getting an error saying i've got an invalid relational operator..

arggh!!!

thanks in advance..
Kathryn