Not sure about this word, but the English language does not have a body that decides what the official words of the language are (unlike the French [0]). It seems that if a word or construct is used often enough, it becomes part of the English language by being included in official dictionaries like the Oxford Enflish Dictionary [1].
Anyways is in the OED with its first recorded usage being in 1560, but it does have this use as any ways, we have to wait until 1784 for it to become a the single word anyways. This use is different than the common modern use and is more a synonym for always, in anyway, in any respect, etc. The modern use does not become common for another 50 years or so and by 1865 we get Dickens putting it to use with the rather good "Anyways, I am glad, etc." Anyhow is also in there along with anywhat and anywhen but no anywho but I am still working from the old Second Edition and not the continuously updated online/soon to be third edition.
Anyways, I think it is safe to say that anyways has been a word in written English for quite some time now.
[0] https://en.wikipedia.org/wiki/Acad%C3%A9mie_Fran%C3%A7aise
[1] https://www.smithsonianmag.com/smart-news/heres-how-oxford-e...
Edit, it is part of written English: https://www.merriam-webster.com/words-at-play/lets-talk-abou....