What is the youngest age a person can be diagnosed with peripheral arterial disease?

Yes: While uncommon people as young as 20 may have peripheral arterial disease, though this is usually the result of a number of vasculitidies such as takayasu's arteritis or berger's disease. More commonly pad is found in people over the age of 50, and quite prevalent in those over age 70. Smoking is the biggest risk factor in developing pad, conferring a 16x higher risk than a non-smoker. Don't smoke.

Worse with age: Pad is due to compromise of the arterial circulation. As we age, there is increased buildup of plaque in our arteries and as this builds up, it narrows the vessel lumen reducing flow. At some point, flow decreases where there is pain which progresses to ulcers, gangrene, etc. It is very uncommon for this to happen when we are young with the exception of rare diseases that accelerate the process.