Question : how to identify when a column was modified

Hi,
   Can someone help me understand how to identify when a column datatype/lenth was modified in the table? Is that possibe?
 

Answer : how to identify when a column was modified

At table/object level you can track when was the last DDL performed.
select last_ddl_time from user_objects where object_name = upper('table name');

But at column level, not possible unless you have database audit options enabled.