When does arteriosclerosis start?

Early: The process of atherosclerosis can actually begin in our late teens and early twenties; although the consequences may not manifest for many years. Autopsy examination from young people dying in wars and trauma has revealed early signs of atherosclerosis in these individuals.

Early in life: Atherosclerosis is a disease that takes years/decades to develop but symptoms are uncommon until early/middle adulthood.