With this kind of long term predictions, it's practically impossible to get the numbers right - ie the number of years it will take for resource X to end, how many billion people Earth can sustain, etc. But this doesn't mean that there are no limits to growth (on Earth): in the last 40 years we invented lots of great technologies that improved the efficiency in how we use lots of resources and reduced the pollution created by production, but there is no silver bullet in sight that could make those disappear.

Just like Moore's law, it worked much longer than anybody expected, but in the end we still hit many limits, and we can say for sure it's not going to last forever even if we don't know when it's going to really end.