When I was a teenager, my day job was bringing back the wooly mammoth for dinner
Seriously, though, I was a teenager in the '70s, and didn't really have much trouble finding work (and as the oldest of five with a single mom, believe me, I *had* to work ).
It is, obviously, somewhat harder today, at least in terms of easily available opportunities, and that can be a bit disheartening when it comes up as often as it seems to.
I think the closest thing to a happy medium (between having job experience, and trying to get it) is to go out of your way to let your prospective employer trust that you *are* willing to do the work. Things like just dropping off a resume, and unrealistic salary or position demands aren't going to get you past the part where HR (or the hiring person) just tosses them in the bin. Whether you do it with grunt jobs while a teenager / college student, or as a probie in an entry level 'pro' job, you gotta pay your dues first, and demonstrate that you are actually willing to come in on time, on schedule, and actually do your work.
As someone who sometimes interviews (and 'approves') job applicants, I will say that I won't consider a lack of job experience for an entry level position to be a showstopper, but if they've never held a job, they have to provide some other way to make me think that they're worth a shot.
Things like actual enthusiasm and a well articulated willingness to do the work are a good start. Usually, for entry levels, there's often a probationary period also.
If it's not entry level, you better have some real experience under your belt.
But, there's no hard and fast rule, it's really about how much you're willing to risk on what can amount to a 'blind hire'.
I've hired kids right out of college, with no job experience, who turned into some of the best I've worked with, and I've hired 'experienced' developers and engineers who had good stats, and talked a good interview, but were less useful than a skin rash (after a while, you do pick up on some of the telltales that let you identify them, though).