EOL:Website-activerecord.errors.messages.greater than/qqq

This is a message given in the context of an error. So, for example, this might imply that the value of "Age" is incorrect, because it must be over 18. So the message is presented to the right of the "Age" field and, in red, says "must be greater than 18".

This means that the verb "must" should always be translated as singular, since it refers to "age". The PLURAL template could be useful in this message if the translation includes the word (year(s)), for example, "(the age) must be greater than 18 year/years".