Not graduating from from high school does not have to be end of your life or your career. While you will need to go back to school, there are other options than being in a room with students half your age. One increasingly popular option for students is to go online. There are now more than a hundred accredited programs, and that number is growing rapidly.
One reason that adults choose online high schools is because it is a faceless process. Unless you elect to share your age, few will know that you have children (or grandchildren) of your own. Even if you are at a school that requires students to work together on projects, it is all in your court how much you choose to share with other students.
Some online students, either high school or college, appreciate that facelessness because it allows them a certain amount of freedom. Unlike traditional high school, you do not worry about asking a silly question because no one knows you. You are not worried about looking stupid in front of that person you want to take to the prom! The only worry is learning the material.
You should know that, for various reasons, not all online high schools allow or are permitted to allow adult students. However, many do and you should make sure to clarify with the admissions office at your school of choice that you are an adult student. Trust me, no matter what your age, they will be happy to talk with you and will not be surprised (or judgmental) about your going back to high school.