While some nations are taller as a result of their country’s statistical demographic height (i.e. Russia, the Netherlands), this isn’t always the case. Factors like sovereignty, historical political repression, and economic strength have been shown to impact the personification’s biological age. 

As such, you have personifications with statistically taller heights like Latvia who are only 15. 

The micro-nations, like Molossia, are an entirely different ballpark. Like regular nations, they’re personality and culture based [x]. Their ages aren’t something that can be attributed to a common sense explanation given that Japan shows surprise at Nikko Nikko acquiring micro-nation status. [x]

There’s also the fact that Lithuania expresses surprise at Sealand’s existence, and warns him not to become a full nation as it would be too hard on his “small body.” Latvia also expresses this concern, mentioning how nationhood would be hard on Sealand’s heart because of said small body [x] Put another way, the micro-nations are as a much of a puzzlement to us as they are to the other nations. 

That said, tonight’s theme will be the influence of economic strength on a personification’s age. As mentioned by anon, while lacking full independence, Hong Kong and Macau have still aged because of their successful economies.