The blurb at the top of the nomination tab on each election page (example) now says:
In the nomination phase, any community member in good standing with more than 300 reputation (and 18 or up) may nominate themselves to be a community moderator.
The text "and 18 or up" does link to the official policy that moderators must be at least 18 years of old, so the meaning is clear after clicking through. But in context, without clicking the link, it's a bit confusingly worded. The last number mentioned was a reputation score, and now another number is mentioned without saying explicitly what it's a number of.
Might I suggest a rewording? Perhaps "and at least 18 years of age" or "and 18 years or above" or "and 18 years old or more". At least something to make it explicitly clear that this is about age, and years, rather than anything else (reputation, badges, ...) Even if it seems obvious to you, remember that not all moderator candidates are native English speakers.