Even if it's the oldest 5%, _eventually_ you'd reach even lower than 20 because the population isn't growing at anything near a rate of 5% per year, and so you'd run out of people that old quickly. You'd see an exponential decline in the Canadian population, halving every 14 years. A -5% rate per year is an extremely unlikely thing to keep up for long

Again this is 5% _of deaths_ not 5% of the population. So it's roughly in line with the number of people who die from random accidents in a given year.