The reason why the data sometimes differ between Wikipedia vs. Playboy's official website and books is because Playboy doesn't tell the truth all the time. They admit to Elizabeth Ann Roberts being under 18, because of the legal case, but they make it seem as if it was an accident and that she was nearing 18, when in fact she had just turned 16 and she told me that Hefner knew exactly how old she was all along. They pretend Cynthia Myers posed at 18, but she herself has repeatedly said in interviews and at her official site that she posed at 17 three months before her 18th birthday. 
 
In fact there are a dozen more Playmates under 18 besides those two, and that's just counting the American edition! 
 
Linda Moon is passed off as an 18 year old by Playboy, then and now, but her photographer said she was 16. Another is Patti Reynolds, who was 8 months shy of her 18th birthday when her centerfold got published, based on her undisputed birthdate. 
 
The most recent one seems to have been Penny Baker, who posed at 17 and was published in January 1984, just 3 months after her 18th birthday. Big magazines like Playboy require months of lead time, especially for important features like the centerfold, which are made well in advance of publication. 
 
The Wikipedia data on Playmates is actually pretty reliable most of the time. I don't know if its claim that Gina Goldberg was 17 when she posed in 1981 is right, however. 
 
The current hysteria in the United States and Australia over "teen sexualization" is social engineering by totalitarian-minded people who deny the facts of nature, and it's high time the debate was taken back from fanatics. Otherwise we'll continue to witness the farce of big magazines pretending all their models and actresses are 18 or older (Playboy isn't the only one that's lying) and their subscribers pretending they dislike looking at women before midnight on their 18th birthday.