How do you toughen and disciplined to mentally strong?

Im realizing only I can help myself and my life depends on me. Complaining, living in the past and feeling regret isn't going to change anything. If I don't understand the importance of being an adult and taking on life responsibilities than is just my fault. I think I'm mentally very weak and really seem to be lacking self discipline also. In my family, there are many people who aren't into physical fitness but verbally they are so tough. They know how to problem-solve, excellent communicaters and know how to get things done and chase after something whether it's a business opportunity or money.

I grew up and still am living as if I'm shy child despite I'm already 28. Even my younger cousins are way ahead of me. They are taking risks and working on their life. From networking for job opportunities and attending college to dating and stuff. I keep overthinking all day about my problems but dont take any actions.