These formulas are not the same though in a leapyear.

Data _NULL_ ;
BirthDate ='29Feb2008'd;
EndDate='28Feb2012'd;
Age = intck("year",BirthDate,EndDate)-(put(BirthDate,mmddyy4.) gt
put(EndDate,mmddyy4.))+(put(BirthDate,mmddyy4.)="0229" and put(EndDate,mmddyy4.)="0228" and put(EndDate+1,mmddyy4.)="0301");
Age2=yrdif(BirthDate,EndDate,'AGE');
Put BirthDate=date9. EndDate=date9. Age= Age2=;
run;

BirthDate=29FEB2008 EndDate=28FEB2012 Age=3 Age2=4