How to make 6 partitions of table by 6 months and 7th partion of older than 6 month data?
Possible, but efficiently.  Only works for PARTITION BY RANGE.

Let's say you are starting to populate partition "2106_09" and need to migrate data in partition "2016_02" to partition "Older".  The command would be something like

ALTER TABLE tbl
    REORGANIZE PARTITION `2016_02`, `Older`  INTO (
        PARTITON `Older`  LESS THAN ('2016-03-01')
                 );


(Caveat: check the syntax.)

Note that you will need to construct this with a different partition name and "less than" each month.

But the problem is that it will rebuild "Older", which will take an amount of time based on how big it is.

This . may have some tips and code that is useful.