Adding dates in plpgsql

I have a trigger that needs to do some addition to dates,

CREATE FUNCTION update_dis_record () RETURNS OPAQUE AS '
DECLARE
    tmpYellow INTEGER;
    tmpBan_Starts timestamp;
BEGIN
    tmpYellow := NEW.yellow % 5;
    tmpBan_Starts := now + "14 Days";
    IF tmpYellow = 0 AND NEW.yellow <> 0 THEN
        NEW.length := NEW.length + 1;
        NEW.ban_starts := tmpBan_Starts;
    END IF;

    IF NEW.ban_starts <> null THEN
        NEW.ban_starts := OLD.ban_starts;
    END IF;

    RETURN NEW;
END;
' LANGUAGE 'plpgsql';

The line "tmpBan_Starts := now + "14 Days"; " doesn't work obviously, but
what is the correct way to ad 14 (or any number of ) days to a date with
plpgsql?

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