Slow stream. Difficult to void, and urinary flow is slow.
Prostate enlargement. Benign enlargement may have no symptoms but when it does cause symptoms there is often difficulty emptying the bladder, incomplete emptying, slow stream, getting up at night to urinate.
Many. Difficulty starting stream. Not feeling empty. Having to use the restroom in the middle of the night. Having to urinate frequently. Dribbling, having to go again right after having gone. Small voids. An enlarged prostate would be incredibly unlikely in a 19 yo.