It does create a big baby boom problem. They have a big generation that is going to grow old relatively healthy (unlike earlier generations) and wealthy. They are going to be dependent on a new generation that is much smaller and currently struggling with unemployment. So, the good news is that there should be plenty to do for these people when their parents retire. The bad news of course is that at point the saudi's will have some economic issues of having to produce more with less people, while facing issues with their oil revenue dropping.
Other issues that are affecting them are the fact that their cities are becoming inhabitable due to rising temperatures. Regular temperatures above 50 degrees are not very sustainable. They are apparently already planning to create some new cities to address this.
The political situation is of course the big topic. The royal family's power is rooted in oil money. As that dries up, the geo-political landscape in the region will start shifting. There's no shortage of countries in the region with similar issues and competing agendas to address their issues. E.g. Iran and Saudi Arabia is a war waiting to happen. The proxy wars have been going on for decades with the US and Europe having played no small role in the history of both countries. Weapon exports to the Saudi's and other countries in the region are substantial.