In WWII, almost every RAF single seat pilot had 150 - 200 hours under his belt (the last third usually in the "Harvard" trainer). At OTU you read the "Pilot's Notes", had a good look round, listened to a bit of advice from a QFI, hopped in and flew. (The Spitfire was a welcome change from the Harvard - it was said the the Spit "was a good lead-in to the Harvard". Simulators hadn't been thought of.
Thousands of lads made out all right then - but I admit the F-35 might be a bit of a handful ab initio !