I noticed that almost all my Nana's "friends" became non-existant when she went into a nursing home. She was very alert mentally and could easily visit for hours on end...very few people came. My Mom retired a few years ago and I've noticed that some of the folks she used to socialize with (from work) don't come around anymore either. Out of sight, out of mind? Either way, it's pretty disheartening.
I'm in my 30s. I know a lot of people (many great acquaitances) but consider very few to be close friends.