Ok, I'd like to see what peoples opinion on this thought are.
We know that the reason Richard doesn't age is because of Jacob, yet we still don't know why Jacob has bestowed this gift upon him. Is it possible that Richard somehow helped Jacob imprison the Nemesis in the cabin and that the cabin has been there for a lot longer than we have been led to believe.
Ok so we saw Horace "building" the Cabin in Locke's dream, but we don't know if this was the same cabin that Jacob or whoever inhabited. What evidence is there to say that Horace never finished his Cabin and that the Cabin we see hasn't been there since the days of the Black Rock or earlier?
My theory is this;
Richard was a passenger/sailor/captain on the Black Rock. He kills the Nemesis and locks his spirit in the cabin and creates the circle of ash to keep him in the cabin so that he cannot escape. Jacob then grants Richard his gift and asks him to protect him hence Richard then becomes Jacob's "Advisor".
This could explain Richard's stunned look when he realises Locke was in the crate and he soon realises who was in foot with Jacob. Also, when Richard and Locke meet in the finale, isn't it fake Locke who says "It's been a long time Richard"
If I've missed something or there is something wrong with the theory then please let me know!!!