Is it still possible to get a decent job in academia (specifically physics) nowadays?
I've heard from a couple physics professors and chairs that it's somewhat difficult to find a first position in physics in general
This is a dramatic understatement. I always recommend reading the first chapter of Karen Kelsky's book. She demonstrates that our universities are not in crisis -- that was 20 years ago. Rather, they are in decay. Most departments are not growing; they are shrinking and cutting back. Yet, graduate programs keep pumping out PhDs.
For physics in particular: APS reports that in 2012, 1800 physics PhDs were awarded. In contrast, there are 9400 physics faculty positions total -- about half of which are at institutions with no physics graduate program (i.e., schools that -- with a few exceptions -- focus on teaching rather than research). From this, you can estimate what fraction of physics PhDs end up with faculty research + teaching positions (see also here).
In short: saying you want a faculty position is like you saying you want to join the NBA -- of course you do! But even for the best students, it is a long shot.
I'm concerned I'd be left out without a job if I tried to do so
Now for some good news. 1-year post-PhD, only 4% of physicists are unemployed. The overall unemployment rate for those with a physics PhD may be around 1-2%. There are research positions outside of universities, and there are also non-research positions that are both intellectually engaging and financially remunerative. Further, you should not have to incur debt to attend graduate school. Thus, attending graduate school in physics might be a good choice (financially and otherwise) even without the allure of a faculty position. But it is certainly good to be realistic about the situation; indeed, you might consider subfields, projects, and skills that could lead to interesting work both inside and outside of the university.
Note: this answer, and the statistics therein, refer entirely to the situation in the US.
I'd like to offer a different perspective on this.
I was in your position in 1979, and convinced I was going to solve the unified field theory problem¹ I went to Cambridge to do first a degree then a PhD. But talking to postdocs in the department convinced me that I really didn't want to get on the postdoc treadmill, and even in 1985 there were already mutterings about the terrible job situation in academia. So after my PhD I got a job with a corporate multinational (Unilever) and:
it paid much better than all but the most senior academic posts
I really enjoyed it
So if you love physics you should not let a fear of job prospects in academia put you off. There are companies out there desperate for clever people and there always will be. I ended up moving into an area (colloid science) that was unrelated to my PhD, but the time spent doing my PhD was certainly not wasted. The skills I picked up doing the PhD were valuable in my job, and more importantly the three years I spent doing the PhD were the best time of my life.
As it happens a student who started in my group at the same time I did stayed in academia and is now a Fellow of the Royal Society.
A footnote: I too am active on the Physics SE. The physics chat room is quite active and there are a number of us there who were or are in academia. You might be interested to ask there about people's experiences.
¹ it turned out to be harder than I expected
I think what Zero the Hero said is important to bear in mind too. Like you, I was really interested in theoretical physics at high school. I participated in the physics olympiad, went on theoretical physics summer schools, wrote an expository book on realtivity etc. I was really into it.
After 3 years of undergraduate physics, I switched to pure mathematics and am now beginning a PhD at the intersection of pure maths and theoretical computer science.
Why the change? I realised that the physics I was interested in was at a bit of a dead end. I had aspirations to be a string theorist/particle physicist, but presently the reach of our experiments is so far removed from the theoretical predictions we are making that the latter is starting to border on philosophy. I don't see that changing within the next 20-30 years or so, and even if governments did invest a lot of resources into building higher energy colliders soon, I wouldn't want to support this as there are much more pressing global issues in desperate need of funding.
However there are a number of areas of physics which are becoming increasingly active and have many important applications, including hard condensed matter, soft condensed matter, quantum information theory, nuclear physics. You could be building the next generation of quantum computers or superconductors, coming up with ways to make fusion reactions a more viable source of energy etc. Note that condensed matter is certainly not easy on the maths. It can be as math-heavy as string theory, and some of the mathemtical techniques developed in high energy physics found use in condensed matter (see Ads-CFT correspondence).
Also, I do not think that studying theoretical physics, even to PhD level, will ever be a bad preparation for the job market. You gain lots of analytical and computational skills that are in high demand for jobs in finance, computing, operations research and more. It might not be as clear cut what career you would end up in, say compared with doing a computer science degree or engineering, but there will be plenty of open doors.
EDIT: Also, I should note that if you plan on staying in the states for college, you don't have a pressure of committing yourself to anything at the moment. You probably have at least 2/3 years before choosing a major, during which the current situation will probably iron out and its long-term consequences on academic positions become more apparent. It may also help to audit different classes and speak to advisors once you are in college. They will be able to give you much better advice about your chances in academia, given your abilities, enthusiasm etc.
For the momement, what matters for college applications is to show you are enthusiastic about some subject and really go beyond your school curriculum in it. That's not to say you shouldn't be keeping an eye on other options you might be interested in now, but for students interested in STEM it is much better to have a few stellar points on your application than spread yourself thin looking at different options.