AC 182: The Alliance invades the Sanq Kingdom and takes the capital in one day. King Peacecraft, an advocate of total pacifism, is killed in the attack. Two-year-old Princess Relena is rescued and adopted by the King's friend and aide (Darlian). Six-year-old Prince Milliardo disappears and is presumed dead. (No mention is made of Queen Peacecraft. It seems logical to assume she was either killed in the attack with her husband, or was already deceased.)
AC 189: Thirteen-year-old Zechs Merquise graduates from the Specials' Lake Victoria Academy with the highest marks in the Academy's history.
AC 191: Rebel terrorists seize several prototype Aries mobile suits from the JAP point base in the Pacific Ocean. General Catalonia sends Treize (age 19) and Zechs (age 15) to dispatch the rebels. One of the rebels takes Relena Darlian hostage; Zechs shoots the man in the hand, disarming him. Not wishing to kill in front of Relena, he tells the rebel to run. Zechs recognizes Relena as his sister, though he does not reveal himself to her.
AC 194: At age 18, Zechs receives the first two-rank promotion in the Specials' (OZ's) history, acquiring the nickname Lightning Baron.
Sources: translations of Episode Zero manga; Endless Waltz (OAV/movie & translations of novelization)