A major factor affecting one's ventilatory threshold is their maximal ventilation (amount of air entering and exiting lungs).
Comparison studies of more athletic people have shown that your ventilatory threshold occurs at a higher intensity if you are more active or have been training for that exercise; although, in some cases shorter continuous tests can be used because of rapid alterations in ventilation.
Frangolias DD, Rhodes EC School of Human Kinetics, University of British Columbia, Vancouver, Canada.
Medicine and Science in Sports and Exercise [1995, 27(7):1007-1013]: A government experiment to test ventilatory threshold was held between November and December 2004.
No significant difference was found between mean values of ventilatory and RPE threshold, when they were expressed by parameters such as: speed, load, heart rate, absolute and relative oxygen consumption.