If i accumulate oex from jan to june....and start selling.. lets...

If i accumulate oex from jan to june....and start selling.. lets say august 2014 my ? is...my idea is to try and hold parcels i'd bought in january2014 till jan 2015...so i get the 50% capital gain discount (if i'm in profit of course)....anyway the tax agent i use tells me that is not allowable and the oex shares you bought first...must be the ones you sell first...is this correct?.....to me its like someone owning 10 houses and the taxman dictates to you...which one your allowed to sell first( you must sell you first\ property investment you bought first.......thanks in advance to anyone out there knowlegable in tax laws