Actually I'm wrong again -- as it turns out, the group with the highest percentage of 7+ cup-chuggers is the 50+ group. It looks like caffeine consumption, overall, steadily increases with age.

Assuming caffeine/cup is linear (2 cups =~ 2x caffeine), the second graph you made shows caffeine consumption vesus age. Since average consumption goes down in the last age group, your sample does not show a steady increase with age.

edit: Think of it as an increase in the 7+ category being counterbalanced by a bigger drop in the lower categories.

Must be the addictiveness of caffeine creeping in :-(

No, that happens in about a week or so.

It is probably more like more responsibility = less sleep = more coffee. I am 24, and my obligations to the world mostly consist of 8 hours of work and a few hours of "chores" (cleaning, grocery shopping, etc.) a week. This leaves plenty of time for sleep.

As you get older, you have more job responsibility, you have a bigger house, you have kids, etc. All these things take time, and probably reduce the amount of time you have for sleep. Caffeine must give people enough energy to get it all done.

(Personally, I use caffeine to supplement my wakefulness. It doesn't really help me not be sleepy if I need to sleep.)