I read an interesting article by Elections Canada that did a survey and analysis of this issue. I'll summarize some of it, but do check out the entire article, and also some of their Young Voter info.
Their results showed that in the 2000 election the 18-20 year-olds turnout was 22.4%, while it was over 80% for those over 58. This used to be shrugged off with "They'll vote when they get older", but recent studies show this to be not true. Each successive generation is less inclined to vote than the previous.
So - why is this, and what can be done?