It has been found in cross-cultural studies that girls tend to have higher self-esteem in adulthood, whereas boys tend to have higher self-esteem in adolescence.
Explanation:
Most girls, on their way to adolescence, tend to lose self-esteem owing to the physical changes happening in their bodies.
Once they cross past the phase of adolescence and become mature enough to accept the reality, their self-esteem boosts up back again.
On the other hand, boys naturally have high self-esteem during the years of adolescence. But the same goes on decreasing with the experience of competition that is there in the outside world.