You rang? Here is my opinion:
First off, it will depend on how great your application is. If you don't have a ~3.9+, a 20AA+, and a couple other special things on your application, don't do it. Everyone I know who has successfully done this has basically had an application that walks on water.
Second, you need to talk to the admissions director(s) at your first choice school(s) and ask them how they view early applicants or if they even take them. They told me at mine that it doesn't happen often but they wouldn't look at my application any different, in other words, they don't stamp it in big red ink with "EARLY APPLICANT." If they don't tell you something along those lines and tell you something like, they seriously look down upon applications of people applying early/you will be on a lower tier....Then don't try it, it's a waste of time.
Third, how much do you like undergrad? I am such the gunner-ish type that dental school acceptance was put before everything else but breathing. My parents don't pay for me to study abroad or take fancy cruises to the Bahamas or take wine tasting classes. I don't like partying...My social life was also bad because of being such a gunner (I'm in the process of reviving it now). I had/have nothing left to do with undergrad. If you are having the time of your life, are not in any rush, or want to do something like that, don't do it.
Finally, the application cycle costs thousands of dollars, takes up a ton of time, and causes a lot of anxiety. When it came down to December 3rd last year...I had done everything and was waiting on a call...I had gone from thinking 'it may be a bit of a stretch, but it can't hurt to apply early' to 'I will be apocalyptically pissed if I don't get in.' This is because it took so much effort and I am not a resilient person. You need to be a resilient person who won't be terribly bothered by it. Because regardless, you are going to be looked at in some capacity as a little lower. It will be age if nothing else. So you may have a God-mode app and it will still get rejected. So if you don't think you would roll with a rejection good, don't try it.
I got accepted. I escaped another year of useless college classes, I saved a ton of money, and I will finish dental rather early.
You other questions:
If you don't have a top choice school and don't care where you go. Contact all the admissions people (not a front desk goon) of schools that take early applicants (check websites) and ask them.
Read the DAT section breakdowns. I personally liked qvault, cliffs AP bio, and chads videos the best.
