Hi DreamKiller
Short-necked turtles are relatively easy to sex as females have a much shorter tail than their male counterparts. In most turtles, the cloaca of the male is situated further away from the anal scute of the plastron than in females. Also male EMM are normally considerably smaller than the female.
At 5cm SLC your little guy (I use generically) is to small to sex accurately and you still have a couple of years before you can get a definitive answer.
V