Please go to Settings > Accounting Settings > General and change your closing period to 24, then you can continue to key in for Jan 2016.
**Year 2016 will only automatically created once you do Year End Processing for year 2015, however once you do this you will not be able to change anything for year 2015. As such we advise you do this after you have get the adjusted journal entry. Please backup before you doing this process as it is not reversible.