I think they raised the limit to 64 bit. The limit used to just be 32 bit integer aka 2.147 Billion gold and no higher but developers have raised the limit very high.
I can't be 100% sure but if this were true, the new gold limit would be 9 Quintillion and nobody could reach that in a lifetime, unless they cheat the game. At least you'd be sure you'll never reach the limit. It used to be that after 2 billion, you can't earn anymore gold though.
Of course don't take me 100% since I know not the new gold limit but you can certainly get a lot of gold.