This is quite a common narrative. But it is also very easy for it to become a self-fulfilling prophecy. If you don't believe that it is easy to make friends, it will be harder to make friends. People are social creatures. Smile, laugh, enjoy yourself, and celebrate the people around you; and you will have friends.
> Am I missing out on anything?
Probably, but such is the narrative of life. If you're concerned about unknown unknowns, then do more scary things. If you like programming and art, try skateboarding or maybe join the debate team and do some public speaking. Just do different stuff. You don't have to abandon the things you like, but you have to make time and space to push yourself into places that are uncomfortable.
> What hobbies do you advise me to adopt that I can do in a group, with camaraderie?
Anything with a group of individuals who are working together. Team sports, band, some ROTC, debate, school newspaper, . I would also caution against the impulse to be "better" than everyone else. Camaraderie comes from working together as a team, not from being better than your teammates. There is enough available success in the world to go around. There's no need to step on people to get there.
> Will college be the same or different than high school?
Both. People will still come in all flavors. The amplitudes of their behaviors will likely be different than what you're used to, but the same behaviors will be there.
> Can I have the same kind of youthful fun when I'm an adult?
Depends on how you define "youthful fun" and "adult". The available options of a 70 year old person are much more physically limited than a 17 year old person. And there is some continuous curve that links those two points. But at 70, you've had a lifetime to accumulate wealth (and maybe some time to blow it too), so the 17 year old may be more financially limited than the 70 year old. Do what you can with what you have.