An Ace was a fighter pilot who shot down 5 or more enemy aircraft. If he was already a pilot at the start of the war and died in late 1940 it would be one roughly every 3 months from September 1939 to December 1940, Probably more like to have been during the Battle of Britain which would have been one shot down every 3 weeks.
Of course if he shot down more enemy aircraft than anyone else it must have been considerably more than 5.
The Battle of Britain fighter pilots were incredibly brave, I seem to remember their life expectancy was 4 weeks. some of them, well many of them, were just teenagers. Poor kids.