One of the life lessons I learned early on from skateboarding is that you always want to surround yourself with people that are better than you. I found that to be true of a lot things, including guitar, woodworking, machining, and most other things that have interested me in life. You can learn a lot on your own, however I find that I hit plateaus when I'm not exposed to other people and learning new things.
However, if I look at the hours I've spent on a skateboard, I'd say 70% of it was spent alone. At 45, I don't have any friends that skate and my ability to do wacky shit is gone. Any buddies that I skated with in the 80s and 90s are either long gone or dead. I do talk to people at the skatepark, young and old, but I actually prefer to be there alone. Skating and surfing are the only physical activities I've ever done where I can zone out and get a natural high alone. I never considered either one to be a "team sport" or even a "sport" for that matter; that was part of the appeal to me.