There are always limits. You cannot perpetually grow. Eventually, you will run out of resources. When we ran out of capital, we began to rely more on other countries. Look where that got us.
The limits to are long term growth lie mainly in our own ingenuity. We have plenty of natural resources and we have plenty of people. What we need is people who are well-educated and who are encouraged to come up with new solutions to problems or to come up with new products that people will like. We have enough resources that we can remain prosperous if only we continue to have ideas that will drive our economic growth. The main limit, then, is in the minds of our people. If they are not educated well enough, we will fail to grow in the long term.