(Just wanna throw it out there that, even though I post this as an answer, Pokemaster absolutely has final say on this! I'm simply taking the time to educate those who read so we're all on the same page.)
The "age restrictions" of COPPA and related privacy protection acts and bills are a matter of liability more than anything else. It's also dependent on the disclosure of what information is being collected and stored on servers, if any. In Pokemon Database's case and using COPPA as the standard, due to the technical content of the website it could be debated whether or not this is a website directed at children, and since we do not collect any personal information, the website is under no obligation to age-screen users, since we discourage users from identifying themselves in the first place and keep no record of such details in the signup process.
There is still some degree of change to the signup process that should probably take place to comply with any potential privacy and child protection laws though, just to be absolutely safe: relating to the example, a checkbox added to the signup process signifying "I am over the age of 13" is basically a waiver the user agrees to so that they can't blame the website for any criminal activity dependent on a user being under that age. The user knowingly agreed to it, so they proceed at their own risk, even if they are under 13; it isn't "our fault", pretty much.
An example of how this typically gets handled is similar to how Facebook and Twitter handles privacy! Emails are sent out saying an update's been made to the terms and conditions (in this case, that terms and conditions have been newly implemented to comply with such-and-such laws). Before being able to log in again, every current and future user must view the long contract, click the "I accept" button way at the bottom, then submit.
What that means is all users who submit are agreeing that Pokemon Database holds next to no responsibility for any user's safety and privacy, since we ask for no personal information and every active user claims to be over 13. Since we have no record of information that could ever prove that a specific user isn't over 13, we have no liability for their status as a child under such an age.
Some of this varies country-to-country, and any complications authorities have with a website are resolved either within the country the website's hosting is domestic to, or the country the owner of the website is domestic to.
Source: Certifications in Business Administration, schooling in Business Law, and - of course - I work at an internet service provider!
