What is the legal age for operating a lawn mower or chain saw?

According to my internet searches, there does not appear to be a legal age but it looks like the American Academy of Pediatrics suggests "a prudent guideline for the minimum age for operation of lawn mowers by children is at least 16 years for ride-on mowers and at least 12 years for walk-behind power mowers and hand mowers." http://aappolicy.aappublications.org/cgi/content/full/pediatrics;107/6/e106