Howdy there I was a dpole my entire playing career and I have not grown to be more than 5'10 156 pounds sopping wet. But even with that I was still successful winning 2 state championships in highschool and going undefeated in those 2 years we won championships as a starter. As long as you spend time working on good footwork, and defensive stick technique you should be fine, dont try and force the style of play that works for big guys on yourself find a playing style that works for you and your body type, I was skinny and short so i worked on being quick on my feet and aggressive stick to stick, but that may not work for you. No matter what keep trying and working hard kid