From my perspective there are three main ways hands can look old.
They can look skinny and wasted, the kinds of hands people have in the last days of cancer. That can be helped with adequate nutrition combined with hand strengthening exercises. There are spring things or tennis balls you can squeeze, lifting dumbbells helps, I know one guy who with one hand at a time tosses up and catches a weight from a barbell.
Hands can also look old just from dry skin. Iodine deficiency can easily cause this, and I think vitamin E deficiency can too. It can also be helped with skin cream or if you dont like smearing all up in chemicals you can make your own skin moisturizer from oats and okra.
Hands can also look old from a restructuring of the nearly microscopic natural textures of the skin. I read a clinical paper on it once, they were able to tell how long past smokers had smoked or how old people were by looking at these features. The healthiest skin has like a cross-hatching [think chicken wire] with like a little star in each compartment. The smoke ages the skin. First to go is the little star thing, then lines in one direction from the cross-hatching start vanishing leading eventually to just a bunch of bars, then the bars start vanishing. Get a magnifying glass and you can tell which hand you used to smoke with. The loss of those nearly microscopic features make for less supple more plastic looking flesh.
I've had all three
my hands look fine now but even from three feet away I can tell I smoked with my right hand, I dont think there is any reversing that effect.