I think this is highly dependent on luck. If you're friendly and happen to live near other, outgoing, friendly families, then the odds of befriending them are higher. It also helps to have a friendly spouse (it helps a LOT).
I met someone at Strangeloop because they were a doppelganger of an acquaintance from some years previously. I now realize that I had this attitude like we already friends because of that unrealized similarity. Attitude and any alignment in interests is more than enough, or alphabetical. :)
There was a girl who I couldn't stand in high school... but we bumped into each other in a train station on the opposite side of the country... and hung out all afternoon.
Just being from the same small town made an immediate (but brief) connection
I had the same experience in 6th grade with a friend who moved to Michigan from Iowa. Last names "M" and "O" put us next to each other in class and the rest is history I suppose.
It feels corny to say, but you really can't make old friends.
My best friend for 20 years (we've since fallen out of touch), was someone I met in kindergarten?
How did we become friends?
My surname starts with a "G" and his starts with an "H" so we were seated next to each other