Jennifer has been player closer to 9 years now but she did start at 29. To her credit she approached the sport like an athlete and has always worked with a coach. Very key. She never had to relearn bad habits... She also gives it 150%, often training 8 hours a day. Many told her she would never make it to the pro tour and that only made her try harder. The fact that she has not only made it but into the top 16 is proof of the power of sheer will & determination.
It does help to be a woman, there is much more opportunity for women starting late, than men, simply because it is a smaller nut to crack. I think it is getting harder though as the bar is continually being raised but if your determined enough there is no reason not to try.
I also know Ellen Van Buran came back to the sport after a very long hiatus, she is now in her 40's and another powerful example of this.