The industry has cycles... at your age you don't need to be too concerned about them.
All you can really do over the course of a career is occasionally do a full-court press to get to the next level if there's a hiring boom that you don't want to miss. But you can't always progress fast enough, so sometimes you just ride it out.
If your opportunities are lower at the beginning of your career, it will almost certainly make up for it later... you'll suddenly find your seniority moving fast, upgrade, bigger planes all falling in your lap. It tends to pour when it rains.
Economic and population growth will drive demand for air travel, so you're not only dependent on retirements.
Carbon concerns might slow the industry a bit, but they seem to be developing work-arounds. Most governments cannot severely hamper air travel because the economic damage will be reflected in their tax revenues.
Automation is hard to predict, but anyone with a technical background background can plainly see that it's over-hyped. Worst case, if you fly cargo you might be alone in the cockpit at the end of your career.
As for the mil, yeah don't do that just for the flying part, you need to be committed to the whole program. But be aware that airline operations (and culture) bears some similarities to mil operations (and culture). It's a big responsibility, and grownup rules apply.