My horse is acting strange.?

Ok i have a 13 yr old Quart Horse, he is a really good horse, he is friendly and gentle. I dont ride him a whole lot even though i should but lately i have been riding him more I only ride . The other day I had haltered him and tied him to the gate. I was going to put the bridle on when he all of a sudden started balking and kicking and he almost pulled the gate down. It was not normal for him. I know alot about horses but that was not like him he has been acting really weird the past couple of days.