I am surprised that these negative effects are much more common in the younger age groups. I would expect them to be clustered in older age groups where there may already be some progression towards heart disease, even if minor or undiagnosed.
Could be related to immune response which is generally higher in children and young adults.
It's why some flu strains are more deadly in the young causing cytokine storms.
There may very well be heart trouble in older people but because they may have already been diagnosed or because heart trouble is expected at that age, no one finds it unusual enough to pay attention to it.
Because it is so rare in younger people, their illnesses stand out.