1. Obamacare penalizes small businesses that don't offer health insurance, but if you are on Medicare, you have insurance via Medicare - so they can hire a bunch of retirees and avoid penalties from the mandates and health insurance costs.
2. If you hire a teenager, they may not have a work ethic, but elders who have to work do.
3. Early twenty somethings working at a low level tend to complain that they aren't getting a living wage or demand $15 an hour for minimum wage / basic work. Retirees who need the money will be grateful for the job and not demand more than the work is worth.