I'm not saying it's not, just professionalism I believe is the main factor which is what I usually look for.I'm not saying it is the only factor, but generally it helps. When I choose youngsters and regens I always do a filter search and look for 14+ on natural fitness, determination and work rate. Providing the other main attributes are okish, very rarely do they turn out badly with some good personalised training, tutors and strategic loan moves. Even wrote a thread on it mate. Trust me, determination is important.
Determination is great though because it generally means your team will fight more in games they go behind in.