I am 42 y/o male with testosterone level of 375. Low for my age? Reason for concern?

Low testosterone. Also known as hypogonadism, this condition is diagnosed by blood tests to check hormone levels, and should be done first thing in the morning. In my own practice, I do not and would not administer testosterone replacement therapy without first confirming the diagnosis with properly-timed lab tests.
Symptoms? That's a little low for age but still above endocrine society guidelines for therapy. If you are having symptoms, repeat the lab with a free t or calculated bio available t.