The time gap between elite male runners and elite women runners, generally hovers around 11% with males out performing females. What's interesting is that the gap doesn't take place until about the age of ten when boys start to enter puberty and gain an advantage. Up until the age of ten, boys and girls can compete against each other on equal footing and if you look at the track and field youth records they are pretty much identical right up until the age of ten.
In most sports, youth development is linear and each year the athlete gets a little bit better than the previous year. With boys, this is mostly true. Boys go through puberty and get stronger and faster which means that most boys are running faster their senior year of high school than they were their freshman year of high school. Boys going through puberty can literally sit around and play video games and eat potato chips and they'll still get faster and stronger.
When you get slightly faster each and every year, it's easier to train and stay motivated.
The following link has some great data on how many girls slow down as they enter their puberty years. One of the big takeaways is that VO2 max for boys steadily increases from ages 8 to 16, but will often remain unchanged in girls.
When it comes to running, a high VO2 max is one part of the equation as is body weight. Running is a strength to weight ratio sport. The less body mass you have to move the easier it is to run.
Thus for girls, you'll often see a 5th grade girl who might weigh 60lbs dominating older girls who have gone through puberty but, has the same VO2 numbers, however they might weigh twice as much and be a foot taller in height.
Why do I bring this up? In one word, expectations. I'm the father of a ten year old girl and what I've casually observed in the last year is that girls who enter puberty early have an advantage in sports like basketball or soccer but, a disadvantage in running.
If you have a gifted ten year old runner, this is great and fun to cheer on but, it's wise to keep your expectations in check that your child might not get much faster. In fact some will even get slower. On the flip, I've known girls who were average youth runners who turn into top tier high school runners through consistent training. Once armed with this knowledge you can tamper your expectations and have realistic goals for your runner.
Running is a life long sport and one of the few sports where a child can compete at the age of ten as well as still compete in 40 years later. Keep it fun, have realistic expectations and understand that puberty affects running, sometimes positively and sometimes negatively.