I'm surprised (but in some ways not surprised given the amount of dip shits and trolls on here) that so many people are suggesting that a 14 year old who has been running for 1 year start doing double runs.
This is the last thing you want to do!!! I repeat, do not do start running twice a day!
More is not always better, and for a young person, it can be absolutely disastrous. The kind of people who do this in high school (especially freshman year) nearly invariably:
1) Burnout, both by the end of each season and more generally by the end of high school
2) Get injured, often developing chronic conditions
You will have to learn that there is no magic bullet workout and you have to work within your body's limitations during training. Keep in mind that you have a lot of stress from school, relationships, etc. You can only handle so much stress from running on top of all that. Improvements will come from consistent, smart training. Period.
Also, any workout, in terms of fitness gains, is only worth what you can recover from it. Stacking runs on runs on workouts gets you nowhere. As another poster mentioned, sleep is vital. Get as much as you can.
If you really feel like you can handle more physical activity, something like a little basketball, soccer or something of that nature is probably your best bet. Those types of sports can help you work on fast twitch muscles and core strength without being too taxing overall.
Just please don't listen to LetsRun losers and start running twice a day.