I have to agree. Private school plus compulsive readers.

People who read and love books tend to acquire knowledge more so than those who don't.

And of coure a full life of varied experiences that expose you to people with higher intellect.

Also well educated and intelligent family members. Every member of my immediate family has more education and is more intelligent than I am. But the 5 of us combined would have about 40 years of higher education,with me having the least.