[otrs] AGE is incrementing after the case/ticket is close succesfull by admin or customer

AGE is incrementing after the case/ticket is close succesfull by admin or customer How to stop this ?? after close. how to remove age from first page of customer. what does pending auto clise + & - means with relations to prending date ? where is the work unit caclulated. where can i get detail manual for otrs or simlair concept