I do most of my winter training indoors on the trainer, it sucks, but it is well worth the rewards. Just starting racing and being so young I would lean towards doing more cross training, mainly weight lifting that focuses on your core and legs with maybe some yoga mixed in. I would not focus on the bike until January/February, assuming that like mine your race season will not REALLY start until May.
Given your age and experience level I would recommend steering clear of any real high intensity and sticking with just a nice steady pace trying to log as much time on the bike as you can, while still having FUN. Don't dump it all on in January though, figure out how many hours you can devote towards time on the bike mentally and commitment wise and start at 25% of that in January, SLOWLY increasing your time on the bike as you get closer to April. I would recommend steering clear of anything really high intensity, keeping any type of interval 20 min+. The more time you spend outside the more bike handling experience you will gain, but I too live in the mid-west, so I know that there are many times that getting outside is just not possible. Rollers would be really nice for someone at the point in cycling that you are, they make going too hard really difficult and help with bike handling.
This is my take on where you are at and what I would recommend for a perspective on your direction. I think it is really awesome that someone your age is interested in cycling to the point where you are ready to race, starting at this age CAN lead to something great with cycling. Don't get me wrong there are some strong young cyclist like yourself, but physically cycling abilities really won't be realized until you are in your 20s, so I would recommend focusing less on training to be in great form and more on the sport itself (bike handling, race tactics, and just connecting with local teams and opportunities for young cyclists). You can train your butt off and come out and toast everyone in the junior category, but odds are by the time you are in your 20s and are capable of producing REAL results in performance you will be toast yourself, and will have lost the drive that it takes. On the flip side, you can have fun and train reasonably, come out and still be in good enough form/fitness to compete and race, learning as much as possible throughout the racing season and meeting people who can help shape your future (assuming that cycling MAY someday be a future for you).
Taking the more passive route of just getting miles, getting in good physical shape, and having fun and learning as you race through your 1st couple of seasons will teach you more about racing and will allow you a greater chance of sticking with the sport to the point where you will have the physical ability to really go somewhere. I know to many guys who started where you are and are now at the age where they can really do something with the sport, but just don't have the drive anymore. Think of your cycling path from now until its endpoint as being a race within itself, come out of the gate to strong and you won't be able to make it to the end...
Cliff notes: Have fun, train easy, and learn as much as possible about cycling and racing your 1st couple of years. Once that you have taken natural ability and some easy preparation as far as it will get you, step up the training and see just how far you can go..