It's much easier to make friends at the start of a school year. Or the start of anything really where a new group of people come together and bonds tend to form in that time. Outside of that regular participation in groups tends to lead to friendships but I find them of a shallower quality than the first variety.

From my observations and what I read it seems that most people when they are adults actually have very few friends and there aren't many opportunities to make friends as an adult.

Just as a baseline to compare to I guess...