LAVI
His Alias/49th name
Age 6: Became the Bookman successor and renounce his true name. Traveled with the Bookman. While traveling, he learned martial arts and medication skills; skills needed as a Bookman.
Age 7: Was shot by a stray bullet and was on the brink of death. While he was unconscious, he kept on clinging onto Bookman's hair. After he recovered, he heard a few random remarks from Bookman which included "pulled off", "lessened"
Age 9: Lavi finally exceeded Bookman's height. But Bookman told him "You didn't include my hair length, therefore I still win"
Age 16: Joins the Black Order as "Lavi", Kanda nearly sliced him apart until Lenalee rescued him. Met Finder Doug [novel only].
Age 18: Reunited with Doug during his mission [novel only]. Went to RewindingTown and met Allen and Miranda.

LENALEE LEE
Have no memory of anything before her parent's death.
Age 6: Found to be a conformer of the Innocence and was brought to the Black Order. First person that she talked to was the Matron.
Age 8: Kanda joins the Order. Mistaken Kanda for a girl . Learned the Zen Meditation.
Age 9: Had mental illness and was confined
Age 10: Reunited with Komui who joined the Order. Learned how to be a lady from Jeryy. Reever and Bak met Lenalee
Age 12: Started helping out the Science Division due to her missions, and soon, became the Chief's assistant
Age 14: Lavi and Bookman joins the Order. Stopped Kanda from killing Lavi.
Age 16: Allen joins the Order. Stopped Kanda from killing Allen.

KANDA YU
Age 10: Became Tiedoll's pupil. Travelled with Tiedoll around the world for a year before going to the Black Order. Met Lenalee (8 years old) and fellow pupil, Marie.
Age 12: Komui joins the Headquarters as the Science Division chief. Daisya Barry joins the Order. Jeryy becomes the Head Chef. Ate Soba for the first time and was touched by the delicious taste, and ever since, he had Soba for his daily three meals
Age 16: Lavi joins the Order. Nearly decapitated Lavi for calling him Yu-kun after Tiedoll
Age 18: After his mission at the forest [novel only], he returned to the Headquarters. Thought Allen was an Akuma and drew his sword against him.

Have no memory of his real parents. Only knew that he was an abandon child. Before activiating his Innocence at the age of 10, he couldn't move his left arm.
Age 7: Met Mana and travelled together with him
Age 9: Played the Pierrot and visited all sorts of places with Mana
Age 10: Mana died. On Christmas eve, he made a contract with the Earl of Millenium and turned Mana into an Akuma. His Innocence activated for the first time and destroyed Mana. Met Cross.
Age 11: Travelled with Cross, learns how to control his Innocence
Age 15: Cross disappeared in India. Found the right markings to the Black Order and became an Exorcist.