Not necessarily. Being 14, your body is in a prime state to develop the muscle fibers (amounts and types) that you will have for life. Take advantage of the growing period and focus on the big compound lifts to increase your fast twitch (IIa and IIb) fibers as these are the largest muscle fibers.

In my personal opinion, at your age, just eat eat eat. Especially while training, I doubt you'll add much fat if any at all. Good luck to you! Most 14 year olds don't have that dedication! Very admirable. Oh and as a side note, if anyone tells you there is some kind of limit to how much muscle people can gain, you have my permission to smack them. Feel free to gain as much as you like