To begin with, you might as well try learning all the moves for the next test on both tracks.
When it comes time to decide which test to sign up for, if you want to actually pass the tests and not just learn the skills, ask yourself three questions, and answer yourself honestly:
1) How powerful are you?
If you stroke forward from one end of the ice to the other, how many strokes does it take for you to get from one end to the other? If you do crossovers around the hockey circles, how many does it take for you to complete the circle?
Do you get good glide and acceleration from each stroke? Are you comfortable maintaining speed through threes and mohawks (including the step from back outside to forward outside)?
For the pre-bronze tests, compare yourself to the level of speed you see from kids taking and passing the pre-preliminary moves and starting to work on preliminary.
If you can cover the same amount of ice with a comparable number of strokes in a comparable amount of time, it may be realistic to aim for standard-track pre-preliminary and preliminary. If you're more hesitant in your skating, you might be better off with the adult track.
2) How deep are your edges?
Do your curves look more like a C or a (? This will become more relevant with moves on the preliminary/adult bronze test and beyond.
3) How flexible are you?
Can you do forward spirals on flats with your free leg at list hip high already? How about on C-shaped outside edges? More of a challenge, on inside edges?
Can you step directly from a back inside edge to forward outside on the other foot at an angle that makes the turn closer to 180 than 90 degrees?
If speed and edge depth and both these types of flexibility come easily to you, then you'll probably do fine with the standard track, at least for the first few tests. If these things don't come easily for your body at your age, you'd more likely be better off with the adult track.
Speaking from my own experience, I had skated as a kid so I had a head start. I started testing moves on standard track and passed the pre-preliminary easily. Preliminary took me three tries; that step from back inside to a forward outside three was a significant challenge, and forward inside spirals on the preliminary spiral pattern are not that comfortable either.
Prejuvenile is even more of a challenge for me. After the second time I didn't pass it, I decided to aim for adult silver as well, which meant I first needed to pass the adult bronze moves.
At a certain point, even if we can do the moves with comparable technique to teenager or preteen, as adults we're likely to be stiffer and slower. That's why the adult tests define the focus of some of the moves as "continuous flow and strength" instead of "power" as on the standard tests. And why the spirals on edges are saved for the third level of adult test instead of the second.
If you want to pass the standard tests, you'll need to achieve comparable levels of speed/power, edge depth, and flexibility that the kids need to pass those tests. On the adult tests, the rules and the judges will give you a break on some of the things that are most challenging for older bodies.
You know your body and your fear level -- I don't. If your coach is familiar with the adult as well as standard track, he or she could probably steer you best.
If you do decide to stick to adult track tests, you could still work on the moves that are omitted from the standard track to make sure you learn those skills even if you won't have to test them.