How old to smoke salvia?

In some states like Maine 18 is the legal age.

I personally would recommend smoking it NO YOUNGER than age 15, or 16 if the person is a little immature, it is a powerful, introspective experience where you lose all control of everything and get pulled through the experience, it should not be used unless you are completely ready for that. Some people are never ready for that, and thusly, they shouldn't use salvia.