Is building at a young age possible/sensible?

It's a bit of gambling, we also had the opportunity in our early 20s to cheaply acquire a small city plot and considered building a small house of about 90sqm on it. Back then, in total it definitely wouldn't have cost ~150k€, especially since you have endless time and friends for the low income assistance. But we decided against it and rented an apartment instead, precisely because we were still young, not together long, etc...
Well, by now there's a townhouse on the plot, the plot alone must be worth 200k€.

Likewise, I could have mined Bitcoins and been a multimillionaire years ago...

Because in the past the number of average annual net salaries that a house cost was significantly lower than it is today.

Is that really so? Regardless of specific numbers, I always claim that you buy as much house as your own finances allow. Always push everything to the limit, you only build/buy once.

and now the other way around....But you also would have invested your entire equity in Bitcoins at the peak, where many believed that 20k€ per Bitcoin would easily become 100k€ in 3 months.