My father's age is four times that of the army, which means my father's age is three times that of the army. So if I divide by three, that is 30÷(4- 1)=30÷3= 10, then Jun Jun will be 10 this year.

When doing math application problems, we should pay attention to reading the meaning in the problem, paying attention to every numerical unit and keyword in the problem, and fully understanding the meaning in the problem before calculating.