2985 - Xao Jin is born a Homo Magi on New Shanghai Earth Colony.
2992 - 7-year-old Xao is found by Chu Ha and taken in as an apprentice.
3000 - 15-year-old Xao becomes a fugitive that hides his Homo Magi status after Chu Ha is killed in Mordu's consolidation of Magic users.
3005 - 20-year-old Xao sees the Legion of Super Heroes battle the Dominators. He starts using his magic to help people.
Dragonmage is a relatively recent addition to the Legion, having only joined the team in 1992 shortly before the Zero Hour temporal reboot. There aren't a lot of stories featuring him, but he's an excellent choice to include in out newly restarted Legion.
In a team that attempted to not have and power redundancy, the Legion sure had a lot of it. but Xao was totally unique: there simply weren't any magic-wielding heroes in it's lineup, and he was a very well-executed one. When you consider that one of the Legion's greatest enemies was Mordu, a superhuman magic welder it seems like a pretty big oversight to have never added a mage to the team proper.
He really wasn't around long enough to have a deep characterization, but by making him part of the new recruits we can set him up to be a long-standing member of the team.