Mosin,
I think that link to the Bushmaster DCM rifle is expired.
I have one that I got through CMP in 2004 (I think) and it has served me well. It is not "special" in the sense of being one of the best competitive AR-15s out there, but it is good enough that when I hold right and break the shot without flinching, twitching, or moving - it is a 10 or an X. It is on its third barrel and I still shoot it - across-the-course and Midrange.
And 14 may be young but it is a great time to start! Your eyes still work - I don't care if you are nearsighted or farsighted, your lenses are still flexible enough that you can see the sights and target. This will not always be true, so use them now to develop your skill, and when they don't work so well you will still be able to shoot.
Apropos of age, you should also know that there was a young lady who shot at our club who was the highest ranking Junior in Texas until she turned 18 (and was no longer a Junior), and last year earned her CMP Distinguished Rifleman badge - something that some of us will never achieve.
So start now and enjoy!