Kiddo.. I presume ur question is to increase the amount of ejaculate or semen.. Coz in this age i do not think u will have any sperm count issues.. Some things which will help u-
1. First of all mention ur frequency of masturbation.. If u do it daily, only one teaspoon semen will come.. If u do it once or twice a week the amount will be even more larger..
2. If u masturbate and cum off in just 2 minutes, the quantity will be lesser than masturbation for 20 to 40 mins and cumming.. Coz in the latter, the amount of semen will be very large like oye ji said..
3. Do not compare urself with porn industry.. They take supplements to increase their cum and there are loads of camera tricks, editing, visual effects and illusions..
4. From my experience, whenever i am on any protein rich food diet or on a supplement powder for body building, the semen which i ejaculate will be more than the normal.. This is because ur semen in rich in protein.. And this excess protein fuels up the sperm and more comes out.. I dont know the exact biological pathway.. I will read through it and let you know..
So dont worry.. Learn to be satisfied with what u have.. Dont compare.. Relative quantities are always dangerous..;) U get what i mean right??:P