They don't ask your age when you buy the ticket, so you can certainly buy it at any age. I've never noticed that they check our age when we check in either--they pretty much look at the picture ID and that's it. The website says age 65 to qualify as a senior, but I've been buying tickets as seniors since we were 60 or so and nobody has ever questioned us. Another mystery, I guess. We do qualify now, but I've never looked at how they define senior before--I just made the assumption that 60 is old enough, and apparently it is.