Do you and your best friend share many similar experiences? What are they?

I was reading this question about whether it was possible to find a good friend. One person made a point about best friends being the same age as you.

I was thinking about how or why that might be true. The main thing I came up with is that people the same age are likely to have gone through similar experiences to you, and they know pretty much the same history as you.

Do you think best friends need to be very much like you? Do they have to have similar experiences and lived through a similar history? How similar to you is your best friend?