So if you have this dataset:
data have;
consent_date='21MAR2018'd;
format consert_date date9.;
do year=1 to 5;
output;
end;
run;
You can create a new dataset with your two new variables like this:
data want;
set have;
open_date = intnx('year',consent_date,year-1,'same')+180;
close_date = intnx('year',consent_date,year,'same')+180;
format open_date close_date date9.;
run;
Result