Aside from being smooth and plump, a young-looking hand has young-looking skin.  Age spots, brown discoloration, and fine wrinkles are all signs of sun damage that build up over years of exposure. The signs of sun damage on the hands can be alleviated with laser and/or light-based therapies.

Laser resurfacing works to stimulate collagen growth and eliminate pigment.  This leads to a reduction in brown spots and wrinkles. Excellent laser that accomplish these effects include Fraxel and ActiveFX among others.  

In a similar way, photodynamic therapy (PDT) uses a photosensitising cream in combination with light therapy to target certain skin cells that have been damaged by sunlight. This treatment can even reduce pre-cancerous areas termed Actinic Keratoses. 

To summarize the steps to younger-looking hands:

STEP 1: Sclerotherapy to treat unsightly hand veins

STEP 2: Replacement of lost volume with fillers or fat

STEP 3: Skin resurfacing to improve sun damage