Photoaging vs. Chronological Aging
Most of what you call "looking old" is sun damage, not time. Up to 80% of it.
Grounded in the research on Photoaging (Wikipedia)
Two clocks, not one
Chronological aging (intrinsic) is the slow genetic clock everyone runs: thinner skin, less collagen, fine lines. Photoaging (extrinsic) is damage from UV radiation stacked on top. Dermatology estimates up to 80% of facial aging in fair skin is photoaging, not your birthday count. Proof: compare your face to your butt. Same age, totally different skin. The difference is sunlight.
The mechanism: UVA goes deep
UVB burns the surface; UVA penetrates to the dermis where your collagen lives. UV triggers matrix metalloproteinases (MMPs) that chew up collagen and elastin, plus reactive oxygen species that wreck DNA and elastic fibers. The result is solar elastosis: degraded elastin clumps that make skin leathery, sallow, and slack. Chronological aging thins the skin; photoaging thickens and ruins it.