"How the child reacts as an adult to all this? Some of it would depend on the parents if he remembered them. What did they teach him by example? He could be someone who blesses his blessing of long life and chooses to do good, curses it and becomes an angry man who does nothing but hurt those around him, or becomes arrogant and sets himself up as a noble and later, perhaps a politician, someone who can control events and people around him."

I think he would swing through all of those behaviors, that would be the challenge in writing the story- tracing the slow changes of a person's charachter while he is accumulating lifetimes of suffering and joy, having to adapt to a world that is changing faster and faster....

I figure he would have to be a loner- after marrying a few times and watching your wife age and die you probably would give up on long term relationships- 'lifelong' friendships would be a danger- long term friends might notice you havent aged a day in the decades that they have known you.... You couldnt live in the same place for very long...

He would be a nomad, someone that is the jack of many trades- a survivor, sometimes doing good, sometimes doing evil... I think over time a cynicism and bitterness would grow, and it would have to show in his writings.... The story would start with a man confused and a bit giddy about his near immortality, that optimism would slowly fade as the centuries pass, and he - by neccessity- becomes colder and more of a loner, and sees humanity making the same damn mistakes over and over again....

Of course, I know this isnt a new plot idea, Spider Robinson addressed the idea in his crosstime saloon series when an 'immortal' woman comes into the bar and shares her centuries of woe.....
and there are many other examples, but my goal would be to be so detailed, and so accurate that the reader would have to stop and ask themselves- "wait, is this fiction?", but as I said- it would probably be too difficult for one person to do.