The first, smallest, and only odd prime gap is 1 between the only even prime number, 2, and the first odd prime, 3. All other prime gaps are even. There is only one pair of gaps between three consecutive odd natural numbers for which all are prime. These gaps are g2 and g3 between the primes 3, 5, and 7.
Girls usually start their periods between the ages of 10 and 16. Most girls start when they're around 12. As everyone develops at different rates, there's no right or wrong age for a girl to start. Your periods will start when your body is ready, and there's nothing you can do to make them start sooner or later. If you haven't started your periods by the time you're 16, visit your doctor for a check-up.
When does menstruation start and stop? A girl may experience her first period between the ages of 9 to 14. The exact age at which this happens is variable and differs from one person to another. A sexually mature girl menstruates once in every 29 to 31 days. During pregnancy the uterine lining is utilized to nourish the baby in the uterus and hence menstruation does not happen.