Melatonin is a hormone produced by the pineal gland located in the brain, and its production is inhibited by light to the retina and permitted by darkness (reference). It has a lot of effects on the body (reference) but I will stick to just discussing its apparent effects on aging and skin.
Melatonin works as an antioxidant and helps in removing free radicals from the body (reference). Research has shown that free radicals could damage the skin (reference), so I would have to conclude that melatonin could have a part to play in maintaining the beauty of your skin.
It is a known fact that melatonin levels in the body decrease from age, and its decrease has been correlated with some of the effects of aging (reference). As you have mentioned in your question, there is research proving that melatonin could decrease the effect of aging in rats (reference). Also melatonin was found to increase the youthful rhythmic activity in a shrew (reference). In the paper titled melatonin and skin aging it has been stated that
In UV-induced solar damage, melatonin distinctly counteracts massive
generation of reactive oxygen species, mitochondrial and DNA damage.
Thus, there is considerable evidence for melatonin to be an effective
anti-skin aging compound.
Moreover in the paper titled "On the Role of Melatonin in Skin Physiology and Pathology", it has been proposed that
Melatonin (synthesized locally or delivered topically) could
counteract or buffer external (environmental) or internal stresses to
preserve the biological integrity of the skin and to maintain its
So in conclusion, I would have to say that melatonin does have a lot of positive effects on the skin but, given that it is a hormone and there are side effects (reference), it should be used in moderation.