He's at an age where he like's to Test you. This is normal Every dog does this , but it is more difficult with a dominant breed. Just show him that you are still the boss.

if you don't mistreat your dog then he is not going to turn on you! He Will love you and protect you!

they somtimes test you just to see how far they can go, but,if you show clear leadership this won't happen to Often in the future. ( this means that for example in a certain situation  you don't show that you are in control, he Will try to take over.)