Currently we are unable to lock past months in current fiscal year. This feature would be ideal in order to minimize errors ex. entering invoices or making journal entries to previous months which have been closed.
steevens Ortiz
Setup>Settings>Company>System and look for "do not allow transactions dated before: XXXX and fill in the date
You already have this ability. When you want to 'close' a month, go into settings and change the 'do not allow transactions before' date.