This site names this specific group directly, distinct from its medication-related cautions: are under 18, pregnant or nursing.
Unlike the blood-thinner and pre-surgical cautions, which apply conditionally, this site lists this group as a direct, unconditional exclusion — worth reading it as a blanket recommendation rather than one requiring doctor sign-off to override.
This site's footer repeats this directly: talk to your doctor before starting if you are pregnant, nursing, or under 18 — worth reading this repeated placement as this site treating the caution seriously, not as a one-off mention.