Melatonin, a sleeping pill from our brain, is the "oldest" natural PAK1-blocker which inhibits melanogenesis and eventually promotes our longevity. Grape peel and Propolis as well as Vitamin D3 and K2 also are anti-melanogenic and extend our lifespan.

Melatonin, an indoleamine, is a natural compound produced by various organisms, including bacteria and eukaryotes. Its discovery in 1958 by Aaron Lerner and colleagues at Yale Medical School stemmed from the isolation of a substance from the pineal gland of cows that could induce skin lightening (inhibit "melanogenesis") in common frogs.
Since then, a variety of its biological activity was found, including inducing sleep, stimulating immune system, suppressing cancer growth etc, etc. All of these findings stronly suggest that melatonin is a natural PAK1-blocker.
As I have described previously, PAK1 is a kinase, which we found in soil amoeba in 1977, and Ed Maser's team cloned in mammals in 1994.
Around 2007, we found that PAK1-deficient mutant of C. elegans lives 60% longer than the wild-type, and around 2015, we found that melanogenesis depends on PAK1.
Finally, in 2019, Melatonin was found to promote the longevity of C. elegans (as well as mice), proving that this natural hormone is a PAK1-blocking elixir:
REF:
O Karadas, N Ozpinar, E Bilgic et al (2019).
The physiological and lifespan alterations in Caenorhabditis elegans exposed to different dosages of melatonin. Pak J Pharm Sci. 32: 625-630.

For more detail of Melatonin, read the 1996 book "The Melatonin Miracle" by Walter Pierpaoli et al (published by Simon and Schuster), and 1995 book "Melatonin: Your Body's Natural Wonder Drug" by Russel Reiter et al (published by Bantam Books).

Interestingly, grape peel also contains a PAK1-blocking elixir called "resveratrol" (R3).
Propolis, the oldest remedy that Hippocrates in ancient Greece used, is an ethanol extract of bee hives, containing a PAK1-blocker called "CAPE" which we found inhibits melanogenesis and extends lifespan of C. elegans as well.

Although Vitamin K2 is a potent PAK1-blocking elixir for C. elegans, Vitamin D3 is a rather weak PAK1-blocking elixir, mainly because it is inactivated by CYP21 which hydroxylates at position 21. However, a CYP21-resistant D3 derivative called "MART-10" was developed as an anti-cancer drug by a Japanese team around 2007, and we wonder if this derivative blocks melanogenesis or not. If it does, it would be a very potent elixir...