The Timeline of Sabo

Early Life & Goa Kingdom

March 20th: Sabo is born into nobility in the Goa Kingdom to Outlook III and Didit.

Childhood: Endures a strict and loveless upbringing where his parents prioritize their social status and wealth over his well-being. After his mother ignores his injuries from a fight to appease a higher-ranking noble, Sabo realizes he is just a tool for his parents' ambitions.
Pre-Age 10: Sabo runs away from his home in the Elite District and begins living as a vagabond in the Gray Terminal. He meets Portgas D. Ace, and the two bond over their shared dream of becoming free pirates. They spend the next five years stealing from thugs to build a pirate fund.

Meeting Luffy: Sabo and Ace discover Monkey D. Luffy following Ace. Initially, they plan to kill Luffy to protect their treasure secret. However, when the Bluejam Pirates (led by Porchemy) capture Luffy and he refuses to talk, Sabo and Ace rescue him and defeat Porchemy.
The Sworn Brothers: Sabo moves in with Curly Dadan's bandit family alongside Ace and Luffy. The three boys share cups of sake, officially becoming sworn brothers.
Forced Return: Sabo is spotted by his father in town. To spare Ace and Luffy from the Bluejam Pirates, Sabo agrees to surrender and return to his noble life.
The Conspiracy: Back home, Sabo meets his newly adopted brother, Sterry, and learns of the nobles' plot to burn down the Gray Terminal to "cleanse" the kingdom before a World Noble's visit.
The Fire: Sabo tries to warn the residents of the Gray Terminal but is beaten by guards. Bleeding and in despair, he encounters Monkey D. Dragon, tearfully confessing his deep shame of being born a noble.
Setting Sail: Unwilling to live in a "disgusting" city, Sabo steals a fishing boat and sets sail early.
The Incident: His boat crosses the path of World Noble Saint Jalmack's ship. Jalmack shoots Sabo's boat with a bazooka, destroying it and leaving Sabo critically injured and presumed dead by the world (including Ace and Luffy).

Rescue: Sabo is pulled from the wreckage by Monkey D. Dragon and brought to the Revolutionary Army's ship.
Amnesia: Sabo wakes up with severe amnesia, unable to remember his name or his brothers, but retaining a visceral refusal to return to his noble parents. He joins the Revolutionary Army.
Training: Sabo is initially trained by Hack, but his combat skills (honed with Ace and Luffy) are already too advanced. At age 13, Dragon personally takes over his training. He also receives training from Bartholomew Kuma.
Rising the Ranks: Sabo goes on missions with Hack and Koala. Over the years, his immense strength and mastery of the "Ryusoken" (Dragon Claw) martial arts allow him to rise to the rank of Chief of Staff, becoming the No. 2 of the entire Revolutionary Army.

The Tragedy: The Summit War of Marineford occurs. Because of his amnesia, Sabo does not participate to save Ace.
Awakening: Sabo reads a newspaper article detailing the war and Portgas D. Ace's death. Seeing Ace's name and face shatters his amnesia. The overwhelming grief and shock of regaining his memories and losing his brother simultaneously put him in a coma for three days.
The Vow: Upon waking and learning Luffy survived, Sabo resolves to protect his younger brother at all costs, vowing never to live with regrets again. He visits Ace's grave, leaving three cups of sake and a newspaper article about Luffy.

Mission to Dressrosa: Sabo arrives in Dressrosa with Koala and Hack to investigate and stop the Donquixote Family's underground weapons trade.
The Reunion: Sabo infiltrates the Corrida Colosseum and reunites with a tearful Luffy. He takes over Luffy's disguise as "Lucy" to fight in the finals for Ace's Devil Fruit.
Winning the Fruit: In the finals, Sabo clashes with Jesus Burgess and Diamante. He destroys the arena floor, claims the Mera Mera no Mi (Flame-Flame Fruit), and eats it, inheriting Ace's powers and unleashing a massive Hiken (Fire Fist).
Protecting Luffy: As Doflamingo's Birdcage game begins, Sabo steps in to hold off Marine Admiral Fujitora to ensure Luffy's safety. Later, he saves Luffy from being killed by Jesus Burgess, severely burning the Blackbeard pirate.
Departure: Sabo meets the Straw Hats, leaves them a Vivre Card for Luffy, entrusts his brother's safety to them, and departs Dressrosa with the Revolutionaries.

Training & Ambush: Sabo returns to Baltigo to train with his new Devil Fruit. Soon after, the Blackbeard Pirates attack Baltigo (due to Burgess stowing away on a ship). The Revolutionary Army escapes and relocates their base to Momoiro Island.
Pride in Luffy: Sabo reads the news of Luffy's exploits in Totto Land and his new status as the "Fifth Emperor," smiling until his cheeks hurt.

Infiltrating Mary Geoise: Sabo and the Revolutionary Commanders infiltrate the Holy Land during the Levely to declare war on the World Nobles and rescue the enslaved Bartholomew Kuma.
The Empty Throne: While sneaking through Pangaea Castle, Sabo discovers the "Empty Throne" is actually occupied by a mysterious sovereign named Imu.
Saving Cobra: Sabo intervenes to stop Imu and the Five Elders from assassinating King Nefertari Cobra. He attacks them but is vastly outnumbered and severely injured. Cobra sacrifices himself so Sabo can escape, giving him a final message for Luffy and Vivi regarding the "Will of D."
The "Flame Emperor": Sabo successfully escapes Mary Geoise. The World Government frames him for King Cobra's murder. This news sparks rebellions worldwide, elevating Sabo's status to a living legend dubbed the "Flame Emperor."

Lulusia Kingdom: A heavily injured Sabo hides in the Lulusia Kingdom. He contacts the Revolutionary Army to report that he did not kill Cobra, but the call is traced.
Destruction of Lulusia: Sabo manages to sail away with several Lulusian rebel recruits just moments before Imu completely annihilates the island from the map.
The Truth Revealed: Sabo arrives safely at Momoiro Island. In a private meeting with Dragon and Emporio Ivankov, he reveals the truth about King Cobra's death, the existence of Imu, and the destruction of Lulusia.
Vegapunk's Broadcast: Sabo watches and reacts to Dr. Vegapunk's worldwide broadcast revealing the truth about the sinking world and the Void Century, paying special attention when those with the initial "D" are mentioned.