Can you have clogged arteries in 20s from very large amounts of saturated fat if only couple of times a month?

Depends: depends on other lifestyle like sugar intake, exercise, stress, good fats and more. for now probably ok, but work on your health

Depends: There is a subset of the general population (~5%) that carry d defect in their lipid metabolism that makes them more prone to arterial clogging at any level of fat consumption. Within this group are some more,some less involved & a blood lipid profile can be dramatically different as early as their teen years or younger. If you carry such a defect you are more at risk, if not, less a problem.