WHBM, Hambleoldboy,
Yes we were a bunch of spotty faced youths at Hamble in those days, but beware those who claim extreme youth. My years are similar to oldboys, and I remember the youngest on my course, who graduated aged 20. 2 weeks leave then into a BEA/BOAC training course. It was very rare to be cleared to the line before the age of 21.
And then we were kept alive by a very experienced Captain and another more experienced F/O, and if you were lucky, a flight engineer.
Nothing wrong with flying a 727 as a teenager, as long as you have a system that covers and acts as the long stop on the ability level.