Luke used the force before being trained...

I always assumed that the first demonstration of The Force being strong with this kid was on the Falcon when he was learning to use the sabre with the helmet and the blast shield down, and he successfully deflected a series of shots from the hovering drone.

And what happened next, he had to be saved by Han Solo and I pretty sure later he made mistakes in his training and got his ass kicked by Vader. If that were Rey she never would have been taken by the Wampa, she would have blown up all the ATs by herself, she would have been the best student Yoda had ever seen by a long shot and she would have defeated Darth Vader without breaking a sweat.

Luke didn't force grab the lightsaber until the second movie, it was years after he knew he had the force, Rey force grabbed the lightsaber the same day she found out she had the force and she moved it a far greater distance and was able to overpower a sith lord for it. Rey is a Mary Sue plain and simple.