The frustration of being a programmer over forty

I just swiched to work as a programmer but was complained working slow in finishing a project by my boss in the group meeting.

I have been working very hard to make numerious changes over time and it is time comsuming and felt really tired.

Should I keep working on this job? I am a female over forty and the oldest in my group. It is so hard that competing with young people in their twenty or early thirty.

I felt exhausted and helpless. What can I do? what is the best career plan for middle aged folks like me?