2 nights a go i was having sex with my girlfriend and we didnt use a condom but i pulled out quick so thats alright its just when i took it out i comed a lot more then i normaly did is this a sign of growing up more because im only 16 and i think that i have grown up because i got more muscular,shoulders bigger, adams apple
it could be a sign, but it's usually more gradual. The cause is more likely from other things. When you had sex, did you stay sexually aroused for more time than you usually do (did you have sex for a longer amount of time), also, was there a greater period of time in between the last time you came and the time you had sex? Getting more aroused and staying aroused for a longer amount of time almost always results in increase load of semen.
No, your body does not store semen. You have glands that secrete all the fluids to make the semen just before orgasm, and it has been found that longer and stronger arousal makes these glands inject more fluids into the seminal flow due to the increase stimulation.
Other than that, it is common to just have a randomly large load for no apparent reason, or a small one. There is no doubt in my mind, though, that since you are 16, you're sex organs are still maturing.