if something is working as intended within it's bounds, how can you call it broken? and how can you call it broken if you throw circumstances at it when it wasn't designed to react to those circumstances?
FIRST, how can anyone possibly believe this plugin is actually for authentic age verification? it's not -- it was not intended to be. it is a "responsible behavior and liability cushion". in other words, it relies on someone telling the truth to work.
if the content on a site is for 18+ and there is nothing in place to ask a visitor's age before proceeding, then the site provider MAY be liable in some situations (note: i can't imagine any such situations myself). also, it may be important that the provider is seen as acting responsibly.
a great example of this is "e-cigarettes". nicotine products of any kind cannot be sold to minors -- even e-cigarettes -- and that industry is under extreme legislative scrutiny right now. so, adding an age-verification screen is a good way to show scrutinizers that the industry is doing all they can to act responsibly.
if there is an age checking process, and the visitor lies about their age to gain access, then it is fraudulent on the visitor's part -- thereby relieving liability from the provider.
if said site proceeded to sell a product that was illegal to someone under 18 without a more strict age-verification process, that's an entirely different ball game. by the way, the minimum age for having a credit card is 18.
SECOND, if i visited a site that required me to be of a certain age, and i was indeed that age or older, but when i entered my age and made a typo as i was doing it, i would be quite upset to get locked out of a site. in fact, i have done that before, but the site blocked me only to notify me that i entered an impermissible age and allowed me to correct it.
if visitors are not allowed to correct typos while filling out a form, and get illegitimately locked out of a site as a result, i'd expect a lot of upset visitors -- or at least, ones prone to typos.
if a site needs to be very strict about the ages of it's visitors, then it will need to implement a much more advanced process than this plugin.