[sdevonoes]

But, how on earth is someone in their 20s able to afford a mortgage for a decent house in Western Europe?

Even for us, developers, who are supposed to be the top 10% earners, it's rather difficult to afford a mortgage. Let's say you are 28 and live in Germany working as a software engineer. You probably earn around 60K euro/year which means (for singles) around 3K/month after taxes. If you want to afford a house (not a flat) then prices start at around 600K EUR (unless you are OK with going to live to a town in the middle of nowhere in your 20s. There prices lower a bit) and usually mortgages are for around 30 years.

In your 30s, you have some more money saved and probably earn more, and probably you don't care anymore if you have to go to live in a town (you are not in your 20s anymore, so the exiting city-center kind of life could not be so appealing to you anymore)