The wikipedia article on feral children, that is children who have been raised by animals, might be useful: https://en.wikipedia.org/wiki/Feral_child
They often seem mentally impaired and have almost insurmountable trouble learning a human language.
The reference, however, is not to published scientific literature, but rather to a popular science website without further references to credible literature: https://www.zmescience.com/other/feature-post/feral-children/
The wikipedia page also states that there is little published science on the matter. Controlled experiments are obviously non-ethical and abandoned children tend to suffer from a variety of problems, which makes it difficult to isolate what is the cause of any deficiency in language.
However, I found the article
GRIMSHAW, Gina M., et al. First-language acquisition in adolescence: Evidence for a critical period for verbal language development. Brain and Language, 1998, 63.2: 237-255.
which discusses the case of a deaf person without contact to the deaf community, who was then fitted with a learning aid and started learning Spanish.
Quote from the discussion:
We have presented here a case of linguistic isolation in the context of normal cognitive and emotional development. E.M.’s case is consistent with the hypothesis that there is a critical period for first-language acquisition that ends at puberty, if not before.
For further information, I suggest reading the article; you can find a freely available PDF via Google scholar: https://scholar.google.dk/scholar?cluster=5578210677808468823 . For further information, try finding relevant articles that cite that one, e.g. via Scholar https://scholar.google.dk/scholar?cites=5578210677808468823 , and the relevant articles cited in the article itself.
You might also be interested in the critical period hypothesis in general: What are the main arguments for and against the critical period hypothesis, and what are alternative explanations?