A survey from the Pew Internet and American Life Project reports that younger internet users (18 to 24 years-old) are more likely to use Twitter than any other age group.
Research in December 2008 found that users in the 25 to 34 year-old age group where slightly more likely to use Twitter than their younger 18 to 24 year-old cohort, but the young 'uns are now in the lead.
See the graph below:
Interestingly, the study also found that the median age for Twitter users (31 years) is now lower than for Facebook users, which has increased to 33 years. Pew writes,
The median age of a Twitter user is 31, which has remained stable over the past year.4
The median age for MySpace is now 26, down from 27 in May 2008, and the median age
for LinkedIn is now 39, down from 40. Facebook, however, is graying a bit: the median
age for this social network site is now 33, up from 26 in May 2008.
The study also found that that more internet-connected gadgets a user had, the more likely they were to Tweet or update their status. See the graph below:
Read the whole study at the Pew website.