Is Morrison for real?, page-31

That's just not correct. immigration can never be an answer to an ageing population problem - simply because immigrants age too! So unless you plan on continuing to increase the number of immigrants year on year perpetually, then age will eventually catch up. There is a name for that.....Ponzi! Here from macrobusiness:

For more than a decade, the Productivity Commission (PC) has debunked the notion that immigration can overcome population ageing. For example:

• PC (2005): “Despite popular thinking to the contrary, immigration policy is also not a feasible countermeasure [to an ageing population]. It affects population numbers more than the age structure”.
• PC (2010): “Realistic changes in migration levels also make little difference to the age structure of the population in the future, with any effect being temporary“…
• PC (2011): “…substantial increases in the level of net overseas migration would have only modest effects on population ageing and the impacts would be temporary, since immigrants themselves age… It follows that, rather than seeking to mitigate the ageing of the population, policy should seek to influence the potential economic and other impacts”…
• PC (2016): “[Immigration] delays rather than eliminates population ageing. In the long term, underlying trends in life expectancy mean that permanent immigrants (as they age) will themselves add to the proportion of the population aged 65 and over”.

The reason is simple: it’s a Ponzi scheme. It requires ever more immigration, with the associated negative impacts on economic and social infrastructure, congestion, housing affordability, and the environment.