I am 57 years old. MBA graduate with substantial experience in Electrical equipment maintenance. I have also experience in NDT.
My guess is that your age is a stigma, though nobody will admit to you that they won't hire you because of your age. They might not even be conscious that they are discounting you because of your age. Look around the office when you go for your interview. Is it filled with younger, or with older people? Do the regular stuff too: Go on the internet and research good interview skills. Practice with your friends. Ask your friends to critique your resume. Look up the company on the internet and come up with some specifics about why you want to work for that particular company. Yeah, that's a good point Your salary expectations might be significantly higher than someone half your age. Better check into that. Also, I have no idea what NBT is. You might edit your question so that people have a better idea of what your experience is. Good luck!
No one wants to pay you what you are worth.