You mention leisure activities, and I think that begs some clarification. This credit is not designed to encourage people to take part in leisure activities. It's more, in part, to get Canada's youth into the habit of carrying on physical activities. Once you get into the habit, you don't need an incentive after that point to continue. That's part of the reason why age 16 was proposed in this measure.
On December 5th, 2006. See this statement in context.