PL/SQL if-else Statements

set serveroutput on;
set verify off;
declare
a int;
begin
a:=&a;
if a>50 then
dbms_output.put_line('you are old');
elsif a>30 and a<50 then

dbms_output.put_line('you are young');

else

dbms_output.put_line('you are child');

end if;

end;