I'm 30 years old and I have similar feelings, as well. I have been through a lot, and have grown to avoid close relationships. The closer I am to someone, the more they hurt me it seems. This stems from how my family treated me growing up, reinforced by friendships and unhealthy romantic relationships. They have traumatized me, and even the thought of dating again really upsets me. Makes my belly turn into a ball of anxiety. I have a difficult time trusting someone else with my emotions.
I also want to sign up for recreational sports and become healthier, but I'm really insecure and scared to do it alone. Fear of being hurt, rejected, or put down by other people hinders a lot in my everyday life. I still try and work through it everyday, some days I will have more courage than others. But all I can do is try my best to overcome these feelings. One small victory at a time. Like today at lunch I joined into a ping pong game on campus. It's only a small game and I lost the match, but I did win in that it was a positive experience; I laughed and made new acquaintances/friends.
I have come to terms and accepted this about myself. It's nothing that will change overnight. I have many acquaintances, still talk to my family but, I keep them at a safe distance. I try to set healthy boundaries when I can. I need to protect myself and teach others how I wish to be treated. I also try to avoid isolating (as it breeds depression and loneliness). I keep myself busy enough that 'avoiding pain' doesn't cripple me, and I can still excel in other aspects of my life (career, hobbies, music, art etc). I channel it into skills and activities that better myself. I can play guitar by myself, I can teach myself piano by watching videos. I can kick a soccer ball at a net, go for a bike ride/walk. A lot of healthy things can be done alone.
These are a few techniques I've picked up in counselling and therapy sessions over the years.
What we're all going through is perfectly normal and ok, a lot of us share the same feelings and insights.
Just don't let this ever make you feel down and depressed, don't ever beat yourself up for it.