Ugandan girls begin to have sex at the youngest age compared with the rest of East Africa, according to data from the Demographics and Health Survey.

The median age of sexual debut in Uganda is just 16.4, at least a year earlier than in Tanzania, at 17.4 years, and almost two years younger than in Kenya, at 18.2.

The data shows that Ugandan women tend to initiate sexual intercourse about one year before marriage — the median age at first intercourse among women age 25-49 is 16.4 years compared with the median age at first marriage of 17.8 years.

However, girls are apparently postponing sexual relationships, mainly due to increased educational opportunities afforded to them. For example, only 19 per cent of women in Uganda aged 20-24 had had sex by their fifteenth birthday. But among older women (age 30-34), 28.6 per cent of them report that they had already had sex by the time they turned 15.

Men in Uganda tend to start having sex later than women. But because they also tend to get married later than women, they are likely to be sexually active for a period of several years before marriage. The median age at marriage among Ugandan men is 22.7 years, while the median age at first intercourse is 18.1 years — which gives men a four-year window in which they are sexually active but unmarried, about four times as long as women typically have.

In Tanzania, too, and as is the case with age at first marriage, men tend to initiate sexual activity later in life than women. The median age at first sex for men age 25-49 is 18.5 years, about one year later than women

This disparity in the age of first sexual intercourse points at a phenomenon that has been highly criticised but still appears to persist — that of cross-generational sex. The fact that younger girls are having sex when their male age-mates are not is a pointer that the girls are sleeping with much older men, who in turn are likely to have several sexual partners. This drives up HIV prevalence in younger females compared with their male counterparts.

But in Kenya, the reverse is true. Men have an earlier sexual debut than women, a pattern that holds true for most age groups. For example, 22 per cent of young men aged 15-19 had already had sex before they turned 15, compared with only 11.5 per cent of women.

Dr Frank Njenga suggests that this could be linked to drug and alcohol abuse in young men. “Young men are more likely to drink or use drugs, and this could easily result in a sexual encounter.”

The age of sexual debut is also getting younger among Kenyan men — nearly a quarter of young men aged 15-19 had already had sex by their 15th birthday, but among older men (age 25-29), only 16.8 per cent of them report having had sex by the time they had turned 15.

Dr Njenga attributes the lower age of sexual debut to the increasing influence of globalisation on Kenyan society. “My experience, just by travelling around the region is that Kenyans are more impacted by globalisation than their counterparts in East Africa — such as a greater exposure to sexuality in the media.”

But these figures are still far lower than for countries like the US, where 64 per cent of boys and 59 per cent of girls have had sex by their 15th birthday; or the Ukraine, where the figures stand at 47 per cent for boys and 24 per cent for girls.