There is no limit, that is the truth. Be Zen, and train everyday as if there is no limit. Harness the power of the human mind and body and train, as if everyday was one more step in the process of reaching perfection, which of course, cannot be reached, thus, one must always train. Whatever you do, Zen Philosophy of Life is always a good way to seek your personal best.
Remember that even little progress is still progress and that patience is a virtue.