If you read the manual of sql reference-- stoarge_clause, you will notice the statement like this:
Specify the total number of extents, including the first, that Oracle can allocate for the object. The minimum value is 1 (except for rollback segments, which always have a minimum value of 2). The default value depends on your data block size.
Restriction on MAXEXTENTS: You cannot change the value of MAXEXTENTS for an object that resides in a locally managed tablespace