Yes, it is clear that Vitus, Sirius or Indriad is involved in some sort of age-stopping magic, as we saw him Kugearen City (Timetravel) and in Marianette's manor, which is implied to be around the same time period, that being roughly 50 years prior the beginning of the game, and the same happens with Nymiera's arc in Hiyoshi.
That's an interesting thought. I'm kinda curious to how she knew Vitus though since you travel back to Hiyoshi City several decades in the past where she clearly knew him. Close to the present day, if you do Narcissa's quest, you get to see an old photo of Narcissa, a young Geara, and Sirius(Vitus) who looks like he hasn't aged a day at all. This leads me to believe he is definitely the man in the legend