Complex sentence: Entrance to the scheme involved a competitive exam, intelligence and aptitude tests, medical examinations and was exclusively limited to males between the ages of 15 and 17 and a half when the Royal Air Force assumed legal guardianship of the lads as "in loco parentis".
Split into simpler sentences: Entrance to the scheme involved a competitive exam, intelligence and aptitude tests, medical examinations. Admittance was limited exclusively to males between the ages of 15 and 17½ when the Royal Air Force assumed legal guardianship of the lads as "in loco parentis".