Most Czechs have sex for the first time before they are 18, according to survey results announced Wednesday by the Prague based Sexualogical Institute. Results from the previous study held five years ago found that Czechs were 18 or over when they had their first sex. The latest results showed that 42 percent of couples relied on condoms during their first sex compared with only a third doing so in 2008. The biggest source of information about sex, for a third of women and over a third of men, were friends and acquaintances. Researchers pointed out that these were not always the most accurate source of information.