Figure: Internet users by age (Click to enlarge). Reproduced from hereI found an absolutely remarkable report issued by the OECD in the summer of 2008. It has got lots of goodies on OECD Internet usage. Here is the URL
The future of the Internet Economy, a Statistical profile
One graph in the report that was very interesting and it is pasted above. The graph shows OECD countries' Internet usage conditioned on the age-group. It is clear that younger people use the Internet much more than older people.
Now as time progresses the young people will age, and I do not think the young people of today will give up on the Internet as they age. Meanwhile the next generations will be even more Internet savvy than today's youngsters. So the low down is that the next 15-20 years will see a high growth period for OECD Internet broadband demand. There is about 20-30 more years of growth in this space before Internet broadband growth saturates, say, the way Electricity did.