First of all remove all myths & misconceptions from your mind about masturbation
In fact, Masturbation is completely normal & doesn't have any bad effect to the body and mind
And night fall is also a normal phenomena in your age group.
Height & built of an individual is determined by Genetics, Environmental & Nutritional factors and Hormonal
factors (most important the Growth Hormone
secreted by pituitary gland
An individual stops growing in height after the fusion of the Epiphyses (growth plates) of the long bones, which occurs by the age of 19-21 yrs in males.
So...don't worry about all this & stay relaxed
Avoid stress...practice meditation
..this helps in improving concentration & builds up the confidence level.
Also make sure that you are taking a healthy & balanced diet, exercise regularly & avoid stress.
Wishing you a Good Health. Let me know if I need to clarify further.
Thanks & take care.