Through the storyline. At the beginning of part IV, Yune makes him a Vanguard.
Not for Lethe and Ike.
Start part 3.
About 20
Path of Radiance and Radiant Dawn.
You have to destroy all her aura and then finish her with Ike
there is a vanguard(Ike), Arch Sage, Dragonlord, Reaver, Sentinel, Marksman, Seraph Knight, Light Priestess, Saint, Valkerie, and Black Dragon.
"he left never to be seen again" it is implied that he went to hatari.
Yes. He becomes a vanguard at the end of Part 3.
16. He is indeed 16 in path of radiance, but older in radiant dawn.
Yes, Ike is a Fire Emblem character. He appears in FE9 (Path of Radiance) and FE10 (Radiant Dawn), for the GameCube and Wii, respectively. Hope this helps!
You meet him at the end of Part 2, after Elincia's Gambit, in a cut scene
Level up a level 20, 2nd class character. You can't do this to ike, micaiah, sothe, elincia and some other people.