My son was on his high school bike team. The kids, 14-18, had no problem riding at 18-20mph consistently. On standard bikes. The real issue here is WHY are adults buying e-bikes for kids perfectly capable of riding regular bikes (amid a child obesity epidemic in the USA)? Don't get mad at the kids. They are NOT paying for these e-bikes. BLAME THE PARENTS. And fine the parents if their kid rides one and is caught doing something inappropriate. Fine them massively (for failing to actually parent).