As I discuss in this question, by far the most popular school of Hindu philosophy is the Vedanta school, which bases its tenets on the doctrines laid out in the Brahma Sutras, a work by the sage Vyasa which summarizes and systematizes the philosophical teachings of the Upanishads. (You can read the Brahma Sutras here.) But the Vedanta school didn't always have the dominant position in Hindu philosophy; before the time of Adi Shankaracharya the dominant school of Hindu philosophy was the Purva Mimamsa school, which I discuss here. In contrast to the Vedanta school which is devoted to analyzing the Jnana Kanda of the Vedas, i.e. the Upanishads, Purva Mimamsa focuses on analyzing the Karma Kanda of the Vedas, i.e. the Samhitas and Brahmanas.
Now in Adhyaya 6 Pada 7 of Jaimini's Purva Mimamsa Sutras, the defining text of the Purva Mimamsa school, Jaimini discusses a Yagna described in this excerpt of the Panchavimsha Brahmana of the Sama Veda which lasts for 1000 years. The issue is, how is it possible to perform a Yagna for 1000 years? Jaimini considers various potential explanations: that it's a Yagna meant for the gods, that it's a Yagna meant for long-lived human beings, that it's meant to be performed over several generations, and that 1000 years really means 1000 months. He rejects all these explanations and comes to the conclusion that 1000 years really means 1000 days. (Which is not surprising as the Purva Mimamsa school was reluctant to believe anything out of the ordinary or supernatural.)
But I'm interested in Jaimini's argument against the "long-lived humans" explanation. He argues that no human can possibly live for 1000 years; here's what this excerpt from Shabara's commentary on the Purva Mimamsa Sutras says:
But humans cannot live so long...."They can attain longevity by means of medicines." ... No medicines have been found to possess the capacity of prolonging life to the extent of a thousand years. All that they are capable of doing is — the improving of digestive powers, the removal of wrinkles and grey hair, the improving of voice and complexion and the resuscitation of memory ; — they are never found to bring about longevity. — "From the improvement of voice and complexion and other signs, we shall infer a longer life also." — That is not possible, we say. — "Why?" — Because there is the text declaring that 'a man's life extends to a hundred years'[.]
My question is, what scriptures describe medicines to remove wrinkles and grey hair? Because they seem to have existed in ancient India given Shabara's statement.
Page 32 of this book describes an Ayurvedic medicine made from the Amalaka plant, which I discuss here and here, that is said to "transform old men into young, with new hair and teeth, and induce physical power like that of an elephant". But what does Hindu scripture have to say on the subject? Ayurvedic texts would be the best place to look.