What's fuelling the wave of youth protests across Europe?

Young people across Europe are taking to the streets over the cost of living, soaring housing costs, and what they see as governments that aren't working in their interests.
In Portugal, Germany, and France the most recent protests have drawn huge crowds, with some demonstrations turning violent and spilling into looting.
So what's behind the unrest, and why is it flaring up now across so many countries at once?