So, men in his world don't have nipples? Okay.
@GhGod - you forgot about his children. It'll take them 15 years to be old enough, but if the birth rate is good, and half of his children are men, his workload will become a lot more manageable.
Assuming 8 matings per day, that's 365*8/2 ~= 1000 boys after the first year. Which translates to 1 000 000 boys after the 16th year, and the whole world pretty much getting saved by 30th year, when the second generation of boys reaches sexual maturity.