For everyone the "30" comes at a different age bracket...it's fine to have noticed, but ultimately...does it matter? Socialization is not the end goal of our existence. There is no value to try too hard to make new connections for the sake of making connections, nor to be faning the flames of connections that had naturally been grown out of. People change. Sometimes they change together, but most times they don't. Instead of forcing friendship, just enjoy the memories of what was good at the time when it made sense.

I have a feeling that for some people the thought of being alone with your own thoughts is the most ominous and scariest thing to imagine. that is what really needs to be addressed.