Athol Stanhope Forbes was born on April 4, 1912, to William Dick Forbes and Isabella Margaret Barr (born Gibb.) While many sources indicate that he was born in Hanover Square, London, the General Records Office (GRO) reports that he was born in Stratford upon Avon, England.
Records also indicate that he attended “Throwthorne Towers” in Berkshire but this was likely a misspelling of Towers School on Waterloo Road in Crowthorne, Berkshire. Forbes was educated at Dover College, a public boarding school located in Dover in southeast England. At the school, he was a contemporary of Group Captain John Hamar Hill CBE (1912–1997) who was Squadron Commander of 504 Squadron and 222 Squadron in the Royal Air Force (R.A.F.) in 1940.
In 1935, Forbes entered Royal Air Force (R.A.F.) Initial Officer training in 1936 and moved to becoming a Under Training (U/T) Pilot at number 10 Flight Training School (FTS) Ternhill on February 1, 1936. Forbes became an instructor and staff pilot at the School of Army Co-operation on August 28, 1937. This operation provided training for air officers supporting troops on the ground.
In the spring of 1939, Forbes married Ernestine May Yeoman Lorraine Forbes (born Carter) on May 27, 193