In the Classic V19 we could purge data anytime after closing of the financial year end and there are reasons why old data is retain then purged at a later date.
As a manufacturer's warranty age...
I have been onto MYOB support about this today and they say that there is no need to purge old data as the new versions dont grow the file sizes as fast.
As our file is now over 500mb and incredibly slow even on a brand new computer I would love to be able to remove old data to to see if that helps.