If I'm anemic and have slightly elevated cholesterol levels due to hypothyroidism, what are my chances of a heart attack/stroke even though I'm 20?

Life Style. You do not have big problem, as high cholesterol and anemia due to hypothyroidism will get better as thyroid problem is corrected if you watch your weight, eat properly, do not smoke, if get high BP get treated, keep your cholesterol level and sugar in noral range. Than you reduce the chance of heart attac and stroke considerably that's my advice.