team as opposed to athletes' legal nationalities – the various Unified teams and Independent Olympian teams are thus each treated as one nation at that Olympic Games. Biological factors Age The 100 m requires a high level of athleticism and as a result most of the participants in the Olympics are aged between 18 and 35 – which is roughly contiguous with the period of peak physical fitness in humans. Consequently, the vast majority of participants in the Olympic 100 m fall within this age range. As of 2020, the qualification rules prohibit athletes younger than 16 at the end of the year of the Games. The record for the youngest athlete to participate in the Olympic 100 m is held by Katura Marae, who was 14 when she represented Vanuatu at the 2004 Athens Olympics. Merlene Ottey holds the records for both the oldest participant and the oldest medallist, having won bronze at age 40 in 2000 and reached the Olympic semi-finals four years later. (Ottey is also the most frequent participant having competed in the Olympic 100 m an unrivalled six times from 1984 to 2004). The first women's champion, Betty Robinson in 1928, remains the youngest gold medallist for the event at 16 years old, while a 32-year-old Linford Christie became the oldest 100 m Olympic champion in 1992. Gender Since introduction of testing by the IAAF in the early-20th century, female sprinters may be subject to gender verification. This rule was first formally applied to the 100 m at the 1968 Mexico Olympics. No 100 m sprinter has been publicly barred at an Olympic competition. However, there have been historic cases involving two women's medallists: 1932 champion Stanisława Walasiewicz and 1964 bronze medallist Ewa Kłobukowska, both of Poland. Walasiewicz endured accusations during her career due to her appearance, but was never subject to a test. An autopsy following her death in a shooting revealed ambiguous genitalia. Walasiewicz accused Helen Stephens (who beat her in the 1936 final) of being male and, despite there being no relevant rules on the matter, officials performed a physical examination of Stephens' external genitalia and concluded that she was female. Kłobukowska was not tested at the Olympics, thus did not lose her Olympic medals, but was subsequently disqualified at the 1967 European Cup on the basis of having a chromosomal mosaic. Intersex athletes are restricted from competition in the 100 m