Give examples of questions you can ask and questions you can’t ask about such things as physical limitations, age or arrest records and convictions.
The basic answer to this question is that you can ask any questions that are clearly and directly connected to the job for which the person is applying. Other questions should not be asked. Not all questions will actually be illegal, but questions that are not based on bona fide job qualifications might well set you up for a lawsuit.
Looking at the specific categories that you are asking about, there are some questions that are clearly legal, some that are clearly illegal, and others that are in a gray area.
For example, in the area of disabilities, you cannot simply ask someone a question like “What disabilities do you have?” Instead, you have to ask questions that are specific to the job. Therefore, you can ask “Are you able to lift an object weighing X pounds on to a shelf that is Y feet high?” You can ask “Can you perform all of the duties described in this job description?” That way, your questions are clearly related to work.
For age, it is not illegal to ask for a date of birth. However, it simply does not make sense to do so. You are much better off simply asking if the person is over 18 (to avoid child labor issues) or over 21 (if they will be serving alcohol). If there are other job requirements that truly require someone to be over or under a specific age, you may ask, but you need to be sure the requirements are bona fide.
As for arrests and such, arrests are not fair game for questions. An arrest does not show anything about a person’s guilt. You can ask about convictions for crimes, though such questions should ideally focus on crimes that would reflect on the person’s ability to do the job.