Roughly 80% of all childhood asthma occurs before the age of five years. It's more common in boys and is seen predominantly in children who are allergic or come from allergic families.
Approximately 50% of childhood asthma, particularly if it's mild, goes into remission during the teenage years but don't be fooled into thinking this means you've "grown out" of asthma. As many as 30% of these children go on to develop asthma during adulthood.