What are some signs that you are a "loner", for want of a better word?

I am 23 and out of university. In the last month or so I've found that I'm a lot more solitary of a creature than I used to be. Socialisation doesn't really do it for me like it used to. I never had a super high social battery, but now I just find all socialisation quite exhausting. I'm just a lot happier all alone or doing solitary tasks.

I like taking long walks alone, going to the cafe or library to work/read alone, spending the night alone watching a movie or playing a game w some cheese and crackers.

Maybe this is just part of aging. Or maybe, despite being a single urban renting man in a large and bustling city, I'm just not really the kind of person who makes and maintains friends naturally. I dunno. I do worry that this isn't healthy for me developmentally, however. Even the friends I have now feel increasingly distant. My thoughts— the good and the bad— rattle increasingly louder in my skull because these days I don't really confide in anyone close enough to share.

I don't actively feel lonely (most of the time). More and more, I retreat from social functions within an hour or two of showing up.

Can anyone offer any thoughts?