First comment: make sure that shown data step code runs. Yours has errors (fixed).
data have;
input name :$10. age date :$15.;
datalines;
rahul 66 03dec2020
rohit 55 2020nov17
nisha 44 12/10/2020
;
data want (rename=(newdate=date));
set have;
newdate = input(date,anydtdte32.);
format newdate date9.;
drop date;
run;
The Anydtdte (any date ) informat will read many but not all common date formats. Problems typically come when using two-digit years as then a value like 01/02/03 can't tell which is actually the year (or day of the month or month in this case).