If a person is alleged to be delinquent, the age of the person at the time the alleged delinquent act was committed controls the determination of jurisdiction under this subtitle. If a person is alleged to have committed an act under § 3-8A-19.1(b) of this subtitle, the age of the person at the time the alleged act was committed controls the determination of jurisdiction under this subtitle. In all other cases under this subtitle the age of the child at the time the petition is filed controls the determination of jurisdiction under this subtitle. In a delinquency proceeding there is no presumption of incapacity as a result of infancy for a child who is at least 7 years old.