Tattoos should not be visible while wearing your interview attire. A lot has been said lately on the subject of weight requirements. Recent lawsuits against airlines by older flight attendants that were still required to maintain their hiring weight well into their later years have been settled in favor of the flight attendants. It will, however, improve your chances at the interview if you display a figure in good physical condition. The appearance criteria may be very subjective.
Every airline looks for a different type of person.
Some want the all-American look, others want the sophisticate. Still others will want the characteristics most traditionally associated with the regions in which they operate. Each company and each interviewer for that company has a different interpretation of what will fulfill their needs. It's not unusual for an applicant to be turned down by an airline one day, and hired by another the next. One friend of mine was turned down three separate times by the same major carrier, was finally hired by them on the fourth try, and now has over 10 years' seniority.