Can the differences between younger and older adults with CHF be grouped into categories, such as increased number or severity of complications?

Depends on cause. CHF is a symptom which can be caused by many different underlying problems: ischemia, damaged valve, damaged muscle, congenital abnormality, aftereffect of infection or other whole-body medical problem. Severity & outcome are more closely related to the cause of CHF (& ability to repair the damage) rather than the age when symptoms start. A good cardiologist can explain details of what to expect.