Is there a significant difference between the average internet usage of persons aged less than or equal to 40 and those aged over 40? ( data i have is age and internet usage)
There must be a difference, but you have the data and I don't. I suggest you draw a graph of internet usage vs. age. You can probably make some inferences from that. By "usage" do they mean average hours use per day? ..or fraction using the internet at all?
From the data presented here:
http://www.pewinternet.org/trends/User_Demo_1.11.07.htm
it is clear that internet usage decreases with age, but increases with income and amount of education.