Yup... sadly, from the age of 19, it commences, but very slowly
at first. Of course, the older one gets, the faster the
degenerative process! 
And lifestyle factors like smoking, drinking, consistently keeping
late nights, as well as hereditary factors, determine whether the
process speeds up or slows down.
In the States, when autopsies were done on young road traffic
accident victims and/or patients who died from various diseases,
they found plaque already starting to build up in the blood vessels
of those in their early 20's. So the plaque that causes so much
trouble to middle-aged and the elderly folks actually start to
appear as early as when they were in their 20's!
In the US, a few prominent cardiologists actually take Lipitor, a
medicine for lowering cholesterol levels in the blood, even though
their cholesterol levels are lower. This is simply a preventive
measure which does good, and there's apparently no adverse effects
from doing so.
