The question says "how long was or is it since you started your career? Was Is And we say a scary or scared look
It would be helpful if you framed your question more carefully and gave us some information about where it comes from.
Also on this site, you are expected to ask one question at a time and to show that you have tried to research it yourself.
However, both is and was could fit here, depending on the context.
If a university student with limited experience was applying for a new job, the obvious question is: How long is it since you started your career? because the student's career is underway.
If a retired professor was being interviewed about his/her life on television, it is likely that the interviewer would ask: How long was it since you started your career? because the professor's career is over and the interview is looking back on it.
So there is no single correct answer to the question. The tense you choose has to fit the context.
If somebody has a scared look, that person is showing fear.
If somebody has a scary look, they person is likely to frighten others.