Kintner is from
Burien, Washington. She began riding BMX in July 1989 at seven years of age and claimed her first national win in the combined 7–8 Girls Class at the
American Bicycle Association (ABA) Great Northwest Nationals in
Sumner, Washington, on August 17, 1990; it was her first national-level race. She won races at this event on both day 1 and day 2. At the age of nine in 1990, she received her first sponsorship from the Bike Factory, and turned professional in 1995 at 14 years of age. She began riding BMX bikes during her childhood, as her father owned his own BMX track in
Washington. She began competing professionally at age 14 and captured more than 70 BMX wins. In April 2004 she made the switch to full-time mountain bike racing competition. In 2006,
Mike King, a former BMX and mountain bike racer, then director of BMX for
USA Cycling, urged her to return to BMX riding, and in 2007 she did so, with the added prospect of possibly participating in the
2008 Summer Olympics Jill came out of BMX retirement in early 2007, ostensibly to supplement her mountain cross training. She won her first post-comeback race on her first attempt. Despite a serious knee injury, Kintner continued to pursue success in BMX riding. With the objective of being included in the US BMX team for the 2008 Olympics, Kintner switched to BMX riding full-time. On June 2, 2008, she won a spot on the team after coming in sixth at the
Union Cycliste Internationale (UCI) World Championships held in
Taiyuan, China, out of a field of 32 racers, making the top 16. Kintner relocated to
San Diego,
California, in order to train at the
Olympic Training Center, and won the bronze medal in BMX racing at the 2008 Olympics on August 19. Kintner stated it was highly unlikely that she would return for the 2012 Olympics. She claimed she was "bored" with BMX riding and that she felt she had reached her "potential". She did, however, race BMX during the 2003 season and participated in the 2003 ABA Grand National, coming in fifth in the Pro Girls event. She continued to race BMX sporadically well into 2004, while slowly shifting her concentration to mountain-cross. Her last regular BMX race was possibly The NBL Gator Nationals in
Avon Park, Florida, on April 4, 2004, where she finished second in the Elite Women event. Her last race pre-comeback seems to have been the ABA Silverdollar Nationals in
Reno, Nevada, on January 8, 2005, in which she came in eighth. She had previously raced MTB cross country part-time since 1997. ==BMX career milestones==