look , when a younger kid is transformed into a well developed man then adolescence is the bridging between a man and a kid. during adolescence , there is physical , mental and sexual maturation. as a part of sexual maturation , semen formation occurs to make you reproductive. Now try to understand , suppose a tap is on and the bucket underneath is full and neither the bucket is emptied nor the tap is stopped so what will happen?? overflow of water out of bucket . same is with semen, adolescent boys who are mature and semen formation has been active and your seminiferous tubules and vas deferents is full and still semen production is going on ( which is normal and healthy) so it is natural that nocturnal emission would occur. a large percentage of boys who do not masturbate may face this problem but those who masturbate do not. semen is meant for ejaculation only, previously marriages used to be done at 15 -20 years so they had less problems but now the marriages occur at 30 - 35 years so either they have relationships with their girl friends or masturbate etc. you need not to worry about this , all you need to do is to visit a clinical psychologist for counselling.