Given your obvious basic story structure, an old man writing a memoir, I don't think that is bad, though I agree with ReindeerFlotilla that the last sentence belongs in your last paragraph rather than your first. There is a certain amount of repetition, however, and I think the writing could be tauter. Perhaps:
"Since the passing of Revaak Snowcrown, the task of chronicling his life falls to me, for I am the last man to know my lord’s tale from the beginning. As I write this, I will see my hundredth year come to an end, and for the sake of men yet to be born, the tale of my lord’s life must be recorded. I am Rarrys Bryne Goodblood, called the Undying, though I fear the day approaches when I must finally prove the name false. May the gods permit me to live long enough to complete my task before I follow my lord into the grave and whatever grand adventure waits beyond this mortal realm."
Random thoughts:
1) As a general rule, short character names are better than long ones; Is there a good in-story reason for your narrator to have a name that sounds more like a law-firm than a person, or did it just sound cool?
2) What does this mean?: "As I write this, I will see my hundredth year come to an end" Does it mean your character is writing at 23:59 on the day before his birthday? It's vague and specific at the same time, and I found it distracting.