How many laser treatments are needed for age spots or liver spots?

Hello. As I get older, I notice more spots and age spots that look like liver spots appearing. What causes these to form? I heard that some spots on certain areas of the body can be related to health issues. Is that true? How long does laser treatment for spots or age spots typically take? I’ve heard that complete removal in one session might not be possible. Also, I am curious about precautions during the procedure and whether there are any side effects.