Clearly fats increase the amount of cholesterol in our blood, which is a risk factor in heart attacks. On the other hand, cholesterol builds up over relatively long amounts of time.
Is it possible to eat enough fats, so that cholesterol becomes a significant risk factor for heart attacks by the age of 21?
Check out "Blood cholesterol and vascular mortality by age, sex, and blood pressure: a meta-analysis of individual data from 61 prospective studies with 55 000 vascular deaths", from The Lancet, Volume 370, Issue 9602, Pages 1829 - 1839, 1 December 2007. [Ref]
Studies on Hypercholesterolemia (High cholesterol) generally find that
...cardiovascular disease is relatively rare in the younger population, the impact of high cholesterol on health is still larger in older people.
Total cholesterol was positively associated with IHD mortality in both middle and old age and at all blood pressure levels.
The U.S. Preventive Services Task Force (USPSTF) recommends screening above the age of 20 , but Canada only recommends screening for ages 40 or over. [Ref]
Many articles discussing high cholesterol in young men are due to genetic factors (Familial Hypercholesterolemia), not eating habits. See "Coronary flow reserve is impaired in young men with familial hypercholesterolemia" from Journal of the American College of Cardiology Volume 28, Issue 7, December 1996, Pages 1705-1711. [Ref]
So to answer your question, Yes, it is possible to eat enough fats that cholesterol becomes a significant risk factor for heart attacks by the age of 21? However, this is only a high risk if you have a genetic predisposition (Familial Hypercholesterolemia). Cases of hypercholesterolemia induced cardiac arrest are relatively extremely rare in non-genetically predisposed youth, but do exist. [Ref]
As was suggested in the comment to the above answer, the premise "Clearly fats increase the amount of cholesterol in our blood" is not all that clear when you look at the literature. I'm hesitant to make this answer on a skeptics site, because ... well ... you should be skeptical when someone challenges such a long held scientific consensus. Before beginning "Plasma lipid and lipoprotein responses to dietary fat and cholesterol: a meta-analysis" in the American Journal of Clinical Nutrition (1997) [ref] is a meta-analysis supporting the idea that we should be skeptical of the OP's claim. It points out that because of the biochemistry of the body, how much cholesterol we eat has little effect on the amount in the blood (more on this later):
The existence of precise feedback mechanisms balancing the input of exogenous dietary cholesterol and endogenous synthesis of cholesterol in the majority of individuals (139) is a primary reason why a reduction in dietary cholesterol has a relatively small effect on plasma cholesterol concentrations in most patients who are diet-sensitive.
Thus I don't plan to convince anyone that the consensus is wrong, because this would take thousands of pages of going through every single study on this issue. Instead, I'll give you a starting point to see that eating (saturated) fat does not seem to add (negatively) to the amount of cholesterol in the blood.
There seems to be three main sources one could be getting this information from: large scale observational epidemiological studies claiming a correlation, basic theory of biochemistry, and controlled studies attempting to identify a causal relation.
The book Good Calories, Bad Calories by Gary Taubes spends hundreds of pages examining what all the main large scale observational studies claim. These include studies (but are not limited to) such as the Framingham Nurses Study or MRFIT. There are problems with whether or not correlations are significant, meaningful, causal. There are more confounding variables than imaginable. In general, you just can't use the weak correlations found in these studies to draw any conclusions. You need something better.
The most persuasive argument should come from biochemistry itself. If we know some biological pathway, then we are essentially done. Peter Attia has done a huge series on what cholesterol is, whether or not it is bad, and how it gets in our bodies.
Here we run into a subtlety. In the original assumption it is unclear whether the poster thinks that eating fat causes an increase in blood cholesterol because you are eating saturated fat or because you are eating cholesterol. Most cholesterol we eat can't be absorbed to the blood stream because it is in esterified form (it is too large to be absorbed). Most cholesterol in our body is made inside the body (Attia cites "New insights into the genetic regulation of intestinal cholesterol absorption" published in Gastroenterology (2005) [ref]). Attia makes his point as follows:
Eating cholesterol has very little impact on the cholesterol levels in your body. This is a fact, not my opinion. Anyone who tells you different is, at best, ignorant of this topic. At worst, they are a deliberate charlatan. Years ago the Canadian Guidelines removed the limitation of dietary cholesterol. The rest of the world, especially the United States, needs to catch up.
Even basic texts such as Lehninger's Principles of Biochemistry contain how this "de novo" cholesterol production works (5th edition, pg 838) and points out that "Excess carbohydrate in the diet can also be converted to triacylglycerols in the liver and exported as VLDLs" (carbs not fat!) which as a later part of the series by Attia points out is actually a better predictor for cardiovascular disease.
Just a word on eating fat. On p35 of The Great Cholesterol Con, Kendrick says: “How can eating saturated fat raise LDL levels? It is not merely biologically implausible, it is biologically impossible." Maybe this is an fallacious argument from authority, but hold off judgment until after the next paragraph.
Moving on to specific studies. Supposing that eating lots of saturated fat causes a worse cholesterol profile it would be essentially impossible to observe results such as in "Comparison of the Atkins, Zone, Ornish, and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women The A TO Z Weight Loss Study: A Randomized Trial" published in JAMA (2007) [ref] (colloquially called "A TO Z"). The study found that the higher fat diet the participants ate, the better their heart risk lipid profile got. Essentially every study of this kind observes the same trend, and really points to the lack of a link between dietary fat and ("bad") cholesterol. The authors say:
Many concerns have been expressed that low-carbohydrate weight-loss diets, high in total and saturated fat, will adversely affect blood lipid levels and cardiovascular risk. These concerns have not been substantiated in recent weight-loss diet trials. The recent trials, like the current study, have consistently reported that triglycerides, HDL-C, blood pressure, and measures of insulin resistance either were not significantly different or were more favorable for the very-low-carbohydrate groups.
As the study points out in other places, if you are eating a "very-low-carbohydrate diet" then you are necessarily eating a high fat diet.
As for the original question, in a meta-analysis of 16 studies involving high-fat dairy foods (which is what the question was about) called "The relationship between high-fat dairy consumption and obesity, cardiovascular, and metabolic disease" published in the European Journal of Nutrition (2013) [ref] it was found that
The observational evidence does not support the hypothesis that dairy fat or high-fat dairy foods contribute to obesity or cardiometabolic risk, and suggests that high-fat dairy consumption within typical dietary patterns is inversely associated with obesity risk.
There are lots of other studies such as "Saturated fat and cardiometabolic risk factors, coronary heart disease, stroke, and diabetes: a fresh look at the evidence" in Lipids (2010) [ref] where it is found that
Most individual prospective cohort studies have not observed an independent relationship between SFA [saturated fatty acid] consumption and incident CHD [coronary heart disease] ... Two recent systematic reviews and meta-analyses, the first including 9 cohorts (11 estimates) evaluating 160,673 individuals [64], and the second including 16 cohorts among 214,182 individuals [68], found no significant association between SFA intake and CHD risk.
and even the unambiguous conclusion:
These meta-analyses suggest no overall effect of SFA consumption on CHD events.
There are many more, but we'll end here because this is already too long. My answer to the question is No! Excessive intake of butter would probably not result in a heart attack at all, yet alone before the age of 21.
