Thank you for contacting Positive Personal Growth. Congratulations of finishing your degree. I feel its important for you to stop thinking of yourself as a person with no confidence and low self esteem. What you focus on becomes true and so if you can change those thoughts to "I am a confident person" and "I am very confident", these thoughts should help you feel better within yourself.
Thirty is not old to get employment, and if you present yourself with confidence and you are the right person for job they may well offer it to you.
Before you go for your interview make a point of finding out everything you can about the company, what they do, what their company stands for and represents in the community, what is important to them. Be knowledgeable so that should they ask you about themselves you can answer them confidently and they will see that you have taken the time to show your interest.
When you go to the interview go with the attitude "This company needs me, I am the right person for the job" - then go get it!!