Hello, I new to road biking and are looking to buy my first road bike. I have been looking on craigslist for a bike that would fit my budget of 600and found a 54cm 2005 specialized allez for 400. I am 5'6" and am about to grow taller because I am only 16. Would this bike be a good purchase? Thank you for your opinions
That's old Sora shifters on that bike, and nobody likes the ergonomics of it (I've had 2 bikes with it, it's awful). Within your budget you can get better with Tiagra or new Sora and be able to shift from the drops.
hard to tell because there is more to bike fit than your height, but looking at the GT, I would say right now you need a small, since you are growing you may be able to make the medium work with a shorter stem.