That's a very good question. I couldn't find a tutorial specifically about painting someone gold but I did find this:
Photoshop Tutorial: Instant Metallic Effect - Digital Camera Reviews & Photography Tips
I adapted it slightly by making a selection of the model's skin only (using
Select >
Color Range), copying that to a new layer and applying the metallic curve to it (see attachments). You can then experiment with blending the "metallic effect" with the original layer.
I only did this very quick 'n' dirty to see if it would work. Obviously if you take a bit more time and care over it, your results will be far superior.