YEAR(2) is a subject to deprecation since it has ill design.
The replacement is YEAR(4) or just "YEAR" type.

* This patch forbids new YEAR(2) column creation:
  CREATE TABLE and ALTER TABLE create YEAR(4) instead.

* For tables with YEAR(2) columns the CHECK TABLE ...
  FOR UPGRADE command returns:

    "Table upgrade required.
     Please do "REPAIR TABLE `...`" or dump/reload to fix it!"

  or

    "Table rebuild required.
     Please do "ALTER TABLE `...` FORCE" or dump/reload to fix it!"

* For tables with YEAR(2) columns the "REPAIR TABLE" command
  calls "ALTER TABLE ... FORCE" where applicable.

* From now any effective ALTER TABLE command application
  converts YEAR(2) columns to YEAR(4) columns.