Why don't young people's arteries get clogged but when they get old, they may produce artery blockage for instance by lipids?

Tough getting old: As we age, many illnesses become more common. It can take many years for the clogging to occur. That said, younger persons often have evidence of the early stages of artery disease disease.

Plaque begins early: Even children can have fatty streaks in the walls of their aorta. It can take many years for the coronary arteries to get significantly blocked, but heart attacks can occur at the site of moderate plaque as the key step in the process is rupture of a plaque followed by a blood clot forming inside the artery.