I'm not sure that changing body chemistry is the typical explanation for changes with age. Although use of some types of medication can have an impact (Some meds used for reducing blood pressure that relax the blood vessels will allow more heat loss) It's wasn't until two years ago that I noticed more sensitivity to cold. With a thinning of the fat layer under the skin and less elasticity in blood vessels, it's somewhat unavoidable. It happens to people at different times and at different rates, but live long enough and it will happen.