That's what I thought...
I'm not going to say one way or another. Now, if you had been 16, I would have given you the 'too young' spiel.
In answer to your question--what problems: IGF does not close growth plates. It does cause unchecked growth if you were that young. While it could cause you to grow taller than normal (if you took a lot) at an early age, it also causes organs to grow, your hands, feet, and jaw to grow, and you could end up looking like a neanderthal with a thick, heavy brow. The main concern is that the organs enlarge much more than normal because your body is already producing a lot of growth hormones at that age. Most people who have too much IGF at an early age end up having serious health problems later.
Since you are 19 and you say you have matured physically at an early age, there is a chance that the growth plates have closed--but that doesn't excuse you from doing research on your own about IGF. We as adults still have to be careful with this stuff. There is still potential for enlarged organs, hands, feet, brow, and jaw (otherwise known as acromegaly). Just make sure you do your homework before making a decision. If you decide to use IGF, use it wisely.