I don't think anyone really knows the exact figures of how age affects training. Everything is just an estimate formed by options influenced by experiences.
I for one am finding my 18 and 19 year old trainees are getting more pops than my 21 year old both with 48+ mins a week and all 3 around the same level.
But I don't think you can put a number on it :P Only the person/people who wrote the game could tell you an exact number.