I would assume that since JKD is based on your body type and what works for You. Height or weight would not be a negative factor it would be up to your coach/Sifu to bring out the positive in the natural tools of your body makeup and pad the negative with how to handle the disadvantage of your body type, making you at least prepared for it.
JKD is a very flexible strategy or phyiscal philosophy.
No matter what system or no method you practice until you are accomplished/comfortable in it, most feel the way you feel. The guys that you are working with maybe somewhat skilled usually even if you are a beginner 6'7 300+ lbs, you could fall on a unskilled person and hurt them. Ask you skilled sparring mates what you need to do better. I bet they will tell you its not U, but they will need to be faster to get out your way the better you get.
Height and Size can be a negative but it takes a very skilled person to expose that. Right now you just can't catch them before they hit and get out. Tell me that ain't true. Like the previous/Mattj posted stated keep training your day will come.