Although we would expect Internet activity to be dominated by the younger generation, statistics show that a large number of the older generation are also actively participating in Online activities meaning chances of finding Granddad on MySpace are no longer zero.  

From Clickz–  Sizing up the Online Generation Gap  (January 2009)

• Generation Y, those between ages 18 and 32, comprise 26 percent of the adult population and 30 percent of the Internet-using population.
• Generation X, defined as those between the ages of 33 and 44, share some similarities with Gen Y. Like Gen Y, people in this age group are likely to play games online (38 percent); watch videos online (57 percent); get job information (55 percent); send instant messages (38 percent); use social networking sites (36 percent); create a social networking site profile (29 percent); read a blog (34 percent); and create a blog (10 percent). Where those in the 33 to 44 age group stand out is in research.
• The population between 70 and 75 years old has grown the most. In a 2005 Pew Internet study, 26 percent were online. At this time 45 percent of the age group is now online.
• The Silent Generation, defined as those between 64 to 72) uses e-mail (91 percent), while 79 percent of the G.I. Generation, ages 73 and older, uses e-mail.

From Scribd – Pip GenY Internet Usage 2009 (January 2009)

Also check out:

• Friday Fact Box - Over 35's on the Internet
• How to Design for Older Web Users
• Who's on Facebook