Magi became known on the planet shortly after the introduction of Mana ore as they are tied to it, being mutants spawned from prolonged exposure to the substance. The details present on the exact origin and facet is foggy at best but what is generally accepted is they were accepted into society after years of discrimation and many new laws were placed because of that.
Because of their affinity with magic humanity has often employed them with understanding how anomalies are formed and how to best fix and/or benefit from them. They prefer to live in the center of the Millennium city as there are plenty of opportunities to use their own natural abilities to the fullest and because of their residence the city became known as the Magic capital of the world.
Magi are just as biologically and physically varied as humans but are no different in terms of physicality, sharing the same needs and even having similar psychology.
Because of their origins likely being spawned from exposure to large amounts of Mana ore they have a natural affinity to magic. They differ from humans because of this and because of it can use magic without the assistance of Mana ore.
Due to the saturation of mana energy they age very slowly compared to humans, the oldest known Magi having lived to be 180. Not to say this isn't without it's limits as this same elderly Magi can barely keep themselves alive without life support and a steady supply of refined green mana.
Magi are created by either a human exposed long enough to Mana ore or through natural sexual reproduction. Hybrids between a Magi and a human spawn Elves instead, the causes of this are as of today unknown.
Magi have identical physical weaknesses to humans, by no means immortal. The only fortification they seem to possess is a natural resistance to magic, though this is only slight and with sufficient enough exposure can do harm.