Pew Internet reports…
Twitter and similar services have been most avidly embraced by young adults. Nearly one in five (19%) online adults ages 18 and 24 have ever used Twitter and its ilk, as have 20% of online adults 25 to 34. Use of these services drops off steadily after age 35 with 10% of 35 to 44 year olds and 5% of 45 to 54 year olds using Twitter. The decline is even more stark among older internet users; 4% of 55-64 year olds and 2% of those 65 and older use Twitter.