How good can you get? How good do you want to be? There is no doubt that deliberate, directed practice will give you a chance to get better. But and is a very big but, you still have to have the goods. A plow horse can't win the Kentucky Derby, but it can become a faster plow horse through proper training. 10,000 hours is not the answer, it can be part of the answer but if it were just putting in the time then anybody could be a champion and that is not the case. The goal, regardless of your genetic endowment is to maximize your potential through practice. It's not the practice it's what you put into the practice accounts. It must be mindful, purposeful and directed. You have to be willing to take risks and learn from your mistakes. It's not just putting in the time.
What particularly bothers me is that fanatic parents are now quoting the so-called 10,00 hour rule as justification for starting kids training younger and specializing early. I heard of some parents counting back from the NFL draft in what would be their son’s senior year in college in order to figure out how much “time” to put in to accumulate 10,000 hours. I don't mean to burst anyone's bubble. But there's a lot more to it than that, you have to have a certain amount of talent to be good at a chosen athletic endeavor. You must have basic physical literacy, the movement ABC’s firmly established as a basis for sport skill. The key is what you do in practice to bring out and optimize your talent. Build a strong, deep and rich repertoire of fundamental motor skills and choose your parents carefully. Read Ross Tucker’s excellent post on this http://tinyurl.com/7jypaaq for more on this perspective.