I am reading the famous paper of Blanchard,1985. There are some fundamental stuff that I did not really get.
1) Why they call it "perpetual youth"? 2) On page 225, he mentions the cohort size. So, for example does it mean that there are "x" numbers of individual of age 20. But this number x declines when the time goes to infinity? Does it mean that at a given date $t$, there are people with age between $0$ and $\infty$ ?