The mass marketing of plastic surgery is starting to show its age. Lifestyle Lift, a nationwide chain of about 50 cosmetic-surgery centers, abruptly shut its doors earlier this month, laying off nearly 400 employees, its spokeswoman said. Its founder, Dr. David Kent, is "exploring a number of strategies," according to his lawyer, which could include filing for bankruptcy or an infusion of new capital to restart the brand. Fueled by its heavy use of national advertisements, the 14-year-old company with 77 doctors had grown to command a major share of the face-lift market.