This is not reality. Reality of friendship or anything in life like dating is good and bad combined. Sometimes is pain in the *ss to have a close friend or lover.
You probably want something that is perfect, and you idealize it from the distance. Friendship is not complicated, you just spend time with other people, not hard at all.
It is also a routine, you need to gain momentum, it will look hard to break you current routine(that is comfortable, what is called the "comfort zone"), but is not, write down an objective you want on paper and look it every day while doing a little every day to gain momentum.
How could I advice an stranger what hobbies should he adopt. I don't know you, your tastes, I do not know where you life, your country. This is your job.
in places like the US people is isolated by default, one way to improve is traveling to a country that is more social for a while like Spain, Argentina,or Brazil.
Youthful fun? Stop desiring what you don't have. I had fun when I was a kid but right now it is only memory. Only the present exist. And the past is not the future.
There are more important things in life than "fun", read "Man's Search for Meaning" of Victor Frankl.
You could have fun at any stage of your life, you don't need permission from others for that.
What usually happens is that what other people consider fun, is not fun for you and vice versa. I get pretty happy spending time in the Woods talking-discussing about philosophy with other people. Other people consider it boring.