You like to think it's perfectly possible to live to be 120.

Don't you? But the oldest person in the world just died, and she was only 116. The new oldest person is also 116, and you've got to go all the way down to 114 to get to the oldest man. How many people do you think there still are who came from the 19th century? Not too many! But you're saying, surely, there will be many medical advances, so that by the time I get up there, reaching 120 will be quite common, probably even 130 or 140. Admit it! That's what you were thinking!