On EPH page 62 (the sidebar), it says that 1 xp is equal to 5 gp. Could you theoretically trade 1 xp for 5 gp during character creation?
For example, Bob starts at level 2. Could he instead start at level 1 with 5,000 gp?
There is no rule that allows this, and rules that would recommend against it.
XP and gp are supposed to be more-or-less tied together. Dungeon Master’s Guide goes into some detail on this when discussing the wealth-by-level chart and related issues. In short, being an Xth level character isn’t just about having Y XP—it’s also about having Z gp. Because gold buys power, and the game’s balance assumes that the power of an Xth-level character includes the power you buy with Z gold, as well as the class features you get from X levels.
When you expend XP for things, you are effectively trading your class features from the level you delay for whatever you’re getting.
But if you can do it freely, for gp, you end up with more powerful items, but less of your own stats. The game wasn’t designed for that—the entire point of the wealth-by-level guidelines is to keep character levels and wealth roughly correlated. The issue here is skew—a character that is too powerful in some ways, but underpowered in others. And that makes the character difficult for a DM to challenge appropriately.
Which is really the ultimate issue: this character is one that will add additional challenges to the DM. They will have to keep track of your “real” power, separate from your actual level, and then they will have to track how your power is different from expected, and so on. The system design would not recommend adding these additional responsibilities to the DM; the system is trying to handle those concerns so the DM doesn’t have to.
That’s the theory, anyway. The reality is, the system doesn’t do all that great a job handling those concerns. The DM is already going to have to do them. But personally, I still wouldn’t allow it, because even though the system isn’t doing as much as it could (or as much as it claims to do), I still want all the help I can get.