What are the causes of plaque rupture?

Hi everyone again, this is a separate question to my other post.  I'm curious if anyone has any up to date theories on the causes of plaque rupture.

I'm aware that heart attacks are often caused by rupture of soft plaque and this is usually plaque that only occludes the arteries about 10 - 30%.

However, this being the case.......why don't heart attacks generally occur in young people as well as older people?  I know it does in some but i'm talking about the general statistics that the doctors and cardiologist quote.  After all young people are said to be carrying around those lower levels of plaque.....

thoughts?

thanks for listening  :-)