i managed to do so.. as below:
data final_age;
set age_calc;
keep study surveyidnum age Age_Group;
if Age >= 20 and Age <= 34 then Age_Group='1';
else if Age >= 35 and Age <= 44 then Age_Group='2';
else if Age >= 45 and Age <= 54 then Age_Group='3';
else if Age >= 55 and Age <= 64 then Age_Group='4';
else if Age >= 55 then Age_Group='5';
else Age_Group='';
run;
proc freq data=final_age;
table Age_Group;
run;