They predict that there will be 10 Billion people on the planet by the end of the century so I would not loose any sleep over that one.
I would. The global population growth is undoubtedly true - but the population growth is not coming from Western Europe. Along with declining birth rates, Western Europe will, because of population growth elsewhere, continue to have a sustained period of immigration.
If you end up with a two-tier country of old 'natives' and young immigrants, do you think the young immigrants will really want to subsidise the aged through their taxes? There are tumultuous times ahead.