Started a statin 6 months ago. Recent blood test: AST of 42 and ALT of 26. Total cholesterol 168 (HDL 53, LDL 91, TRIGLY 144). Is the AST too high?

Not quite. All laboratory results need to be interpreted in the clinical context and the doctor who ordered the tests is usually in the best position to do that. Talk to the doctor who ordered the tests. Having said that, your AST is at the upper limit of normal and not enough to be concerned about.