There aren't a lot of system administrator positions and most are likely filled by promotion of a qualified internal candidate.
I agree. A system administrator position is going to be fairly high up, not an entry level sort of thing. Usually filled by promoting from within or hiring someone from a similar position.
If you want to aim for that job, then you'll need to start near the bottom and work your way up.
There's a big difference between programming analog systems and trunking systems. It requires some different thinking, although it sounds like you have a good start.
I'd follow the advice above and start looking for shops or agencies that are hiring installers. That's where most get their start. You would need to really have a firm grasp on the fundamentals before they'd let you start programming radios, and before letting you loose on a trunked system.
I've been doing the system admin thing for about 25 years now. It's changed a lot since the early days of analog trunking systems. It's all IP now, and having a really strong networking background is a requirement. If you have a community college near you, start taking networking courses. You'll absolutely need to know that stuff.
It's likely that as a newcomer, you'll get your start in the install bay, so be ready for that. One of the local county run shops hires a lot of guys out of car dealership shops since understanding vehicles and electrical systems is important. A lot of the jobs I see posted are for entry level or install type jobs. There are occasionally higher positions, but they usually have a lot of requirements regarding training and experience.
Once in, you'll probably get opportunities to move up and work in the field. Radio programming takes a while as their is some real trust involved. If you want to work for a public safety agency, it's likely that you'll eventually need background checks, as they'll want to know that the guy that has the encryption keys and full access to the system is trustworthy. My employer eventually ran me through the background checks that they use when hiring 911 dispatchers, since I was touching a lot of the same equipment. Make sure your background is squeaky clean and your financial affairs are in order if you are aiming at a public safety job.
Commercial radio shops are a different story, but there's a lot of them getting shut down, so competition for the available positions is really high. Make sure you have something that makes you stand out.
Some skills to start working on:
IP networking/routing
Electrical/mechanical skills
Fabrication skills
Troubleshooting skills.
Tower climbing certification is often required, either before or after hiring.
These guys would be a great place to start:
ETA is a not-for-profit, 501(c)(6) association that offers accredited and vendor-neutral technical certifications.
www.etai.org
Talk to
@speedway_navigator he's an instructor for them.
Remember, you need to make yourself stand out from the crowd.
Funny thing about my job, though. While doing the system admin thing is in the "real" job description, there's about a million other things that are not. Dealing with electrical/back up power, DC power systems, HVAC issues, site maintenance issues, building issues, and a ton of other things that you'd never imagine, sometimes that's what takes up most of my day.