A popular solution to the problem of population aging is to simply increase the rate at which we admit immigrants. This sounds reasonable: the age profile of new immigrants is generally younger than that of the existing population. But increased immigration can't do much more than make the problem slightly less bad. (See also this CD Howe Institute study.)
The number of youths entering the workforce is now less than the number aging out of it, and this gap is going to get bigger as time passes - see this post.
Here is is the age distribution of the population of the 2009-10 immigration wave. The population numbers are as of July 1 of a given year, so these are the immigrants during the year preceding the 2010 numbers.
The age distribution of new immigrants is concentrated in the 25-40 year old range, which corresponds almost exactly with the dip in the profile for the working-age population. Clearly, immigration can and does attenuate the effects of population aging.
The problem is the scale of the vertical axis. 9000 additional 30-year-olds makes barely a dent in the age distribution:
Just to bring the point home more clearly, here's what you'd have to do to fill in that gap to the left of that peak at age 47:
To put those numbers in perspective, the gross flow of immigrants in 2009-10 was 270,000 people.
Reshaping the population profile so that it is non-increasing throughout involves adding an additional 6 million people. And there's not much point in talking about gradually increasing immigration: the hole increases by 200,000 per year as the population peak moves to the right.
Higher immigration rates can't hurt and will likely help. But we shouldn't be under any illusions about just how effective increased immigration will be in dealing with population aging.