This argument is missing the point - the questions is not how many people will be of age X in 2040.
It is about how many homes will be released due to owners passing away in 2020 vs 2040.
The very fact that there will be more older people in 2040 also contributes to getting more homes released.
What the statistics does not even consider is what happens if we manage to extend life, even by say 10 years. A completely different picture emerges where homes get even more expensive.