I am still friendly with a group of girls (about 5 or 6) who were in the same class as me at senior school, one went to the same infant/junior school too. I am sixty years old, in fact we all hit 60 years this year. Some I keep in contact with more than others, some years pass by and I might only see them once, usually phone more often. We dont live near each other, but when we get together we have a real good chat, and seem to be closer just because we have known each other so long. We talk and laugh about school, we know each others parents, one friend came to my dad's funeral, and I went to her mother's funeral and her daughter's wedding.
I also keep in touch with two friends that I went to college with, alto one of them died in her late 40s. And one friend that I worked with many years ago.
I have other friends that I have made along the way, but I think that the shared past experiences over so many years with my school friends, the birth of our children, our marriages, our divorces (in some cases) retirement, give us a very strong friendship bond. I find we can pick up the friendship just where we left off, even though months may have gone by in between.
Oddly enough none of my school friends lived near me, either today, or when we were at school together. But we still manage to get together, and four of them, two husbands and one with her daughter and two grandchildren all turned up at my "surprise" 60th party recently.