Chronology of Young Xehanort:
① [3D] The man in the brown robe gave up some of his power giving Young Xehanort the ability to travel through time.
※Connects to Young Xehanort ③ via Time Travel.
② He left his home on Destiny Islands and trained vigerously at the Land of Departure along with his fellow pupil Eraqus. He eventually grew old.
※Connect to Master Xehanort ①
Young Xehanort from the future who came to this era had lost all of his memories and experiences. However, all of his actions to this point (the path he intended to follow) was etched deep in his heart and propelled him to travel from the islands.
③ [BbS FM] Traveling through time to the Land of Departure, he faces off with Terra, Aqua and Ventus.
※Connects to Young Xehanort ④ via Time Travel.
He appears in KH BbS FM as a mysterious man. Due to being prior to his training, he does not summon a Keyblade. Also, in KH BbS FM there is an enemy "No Heart" who wields Master Xehanort's Keyblade and wears armor similar to that of Xemnas.
④ [Re:coded] Traveling across time he proceeds to Radiant Garden to secretly speak with Braig. He then proceeds to take the recently reverted to human version of Saix (Isa) somewhere.
He joins as a member of the True Organization XIII and retrieves Isa. Because of the X-like mark, what looks like a Recusant's Sigil on Isa's face may be one of the reasons Young Xehanort took interest in him.
⑤ [3D] He leads Sora who was traveling through worlds trapped in sleep into the depths of dreams.
Young Xehanort was aware of his own path beforehand and thus watches and waits until Sora falls into a deep sleep. That consciousness became shared among all the Xehanorts and others such as Ansem, Seeker of Darkness and Xemans unknowingly began seeking out what was necessary to forge the χ-Blade, such as the 13 Darkness and the 7 Lights.
⑥ [3D] He waits with the members of True Organization XIII for the arrival of Master Xehanort before returning to his own time period.
※Connects to Young Xehanort ② via Returning to Own Time.