Hi -- Definitely! If that little voice keeps perking up, do something positive with it!
ACE and AFAA are both widely respectable -- I'm not really familiar with group fitness certifications other than those two. I was certified thru AFAA in '99. For my first exam, I had to go to a testing location led by an AFAA presenter -- I took a written and practical exam. Now, when I renew my certification, I can just go online, pay $200 for a 2-year renewal, answer a chunk of questions, and I'm set. I'm not sure you can do an online exam via AFAA now for your *first* certification. (P.S. My first instructor certification on location thru AFAA was ridiculously easy...)
Either way, the exam doesn't teach you to teach. Whether you go ACE, AFAA, etc., the important part is knowing how to teach, to connect with your class, to keep up the "flow" throughout class.
Go pick a couple gyms of interest (if you haven't/don't already), take classes, and find out if you could team teach with a fave instructor once you are certified. For example, once certified, you could teach the warm and stretch of a class. And, say it's a weights class, maybe you could teach to one tune upper/lower body exercises. And so on...build from there.
Know that it really just takes practice. Definitely find a caring instructor who doesn't mind you sort of emulating his/her class. And, take note of how different instructors build their classes -- i.e. how much time they take for warming up, for cardio portions, how they build the pattern of their cardio portions, etc. etc. etc.
Once you're certified and beginning to teach, remember to be yourself. Make eye contact, be real, and teach your own style!
