What is the origin of the idiom "good as gold" and when to use it?

The origin of the idiom "good as gold" is unclear. However, it likely stems from the association of gold with value, purity, and positivity. Gold is often used metaphorically to represent something valuable or precious, and in this case, it represents good health and a positive attitude. It is used to suggest that the person is in excellent physical condition or possesses a cheerful and optimistic attitude.