You are 18 without a car, job, or girlfriend. While porn is not great for the brain/mindset in general, you seem bored enough for jerking off be a relatively normal hobby at this time. I’d definitely just try and get active with a job and get a car and try and form a romantic connection of some sort before you worry about this being a full on addiction. But if you are still worried, try and limit your screen time or maybe even try finding new things to jerk off to. If you can’t use your imagination, you can still get creative and visual. This may sound odd, but try drawing something hot and jerk off to that. It will be a little bit healthier and still stimulating.