Doing a verification of age is pretty difficult when it comes to websites, and virtually no way is 100% fool proof aside from making someone send in a photo copy of their drivers license/Id, social security card, and mail sent to their residence.
The most logical, and common way to attempt to verify someone is over the age of 18 is by credit card, and asking them to pay a small fee. That assures that there is a good probability that they are either 18, or at least have their parents consent to use the credit card for access to the site.
All of that could be done fairly easily by adding the member subscription module to your site when you purchase a plan, or adding it to your existing plan if you already have one.
